Protection of lithium-ion batteries (Li-ion protection controller). Protecting car batteries from overcharging Li ion protection controller

Since I quite often reviewed batteries, and also mentioned the modification of cordless tools, in private messages I am often asked about certain nuances of modifications.
Different people ask and the questions are often about the same, so I decided to make a short review and at the same time answer some general questions related to the choice of components and reworking batteries.

Perhaps the review will seem incomplete to some, since only the battery itself has been redesigned, but don’t worry, I plan to make the second part of the review, where I will try to answer questions about remaking the charger. At the same time, I would like to know what the public thinks is better - a universal board combined with a power supply, a board on its own, DC-DC boards or other options.

Screwdrivers, and just any other cordless tool, have been produced for quite a few years. Therefore, users have accumulated quite a large mass of both old batteries and tools that sometimes lie like dead weight on their hands.
There are several ways to solve this problem:
1. Just repair the battery, i.e. replacing old elements with new ones.
2. Conversion from battery power to mains power, up to installing a power supply in the battery compartment.
3. Replacement of Nickel-cadmium and Nickel-Metal hydride with Lithium.

As a small aside, sometimes there is simply no point in remodeling/repairing. For example, if you have a very cheap screwdriver, bought at a mega sale for 5 bucks, then you may be somewhat surprised that the cost of remodeling will be as much as several of these screwdrivers (I’m exaggerating). Therefore, you must first estimate for yourself the pros/cons of the alteration and its feasibility; sometimes it is easier to buy a second tool.

Many people have probably already gone through the first option, as did I. It gives results, although in the case of a branded tool it is often worse than it was originally. In terms of price it comes out a little cheaper, in terms of labor intensity it’s simpler and significantly easier.

The second option also has a right to life, especially if you work at home and you don’t want to spend money on replacing batteries.

The third option is the most labor-intensive, but can significantly improve the performance characteristics of the tool. This includes an increase in battery capacity and the absence of a “memory effect,” and sometimes an increase in power.
But in addition to being labor-intensive, there is a side effect: lithium batteries perform a little worse in cold weather. Although, given that many companies produce such a tool without problems, I believe that sometimes the problem is exaggerated, although fair.

The batteries have different designs, although in general they have a lot in common, so I will tell you and at the same time show the example of one of the representatives of this category, the Bosch PSR 12 VE-2 screwdriver. This screwdriver is a friend of mine, and he also acted as a “sponsor” of the review, providing the screwdriver itself, batteries, a protection board and consumables for the modification.
The screwdriver is quite good, it has a spindle lock, two speeds, so it makes sense to redo it.

It so happened that there were even three battery packs, but we will remake one, I’ll leave another one for another review :)

By the way, the batteries are different, but both are 12 Volt, capacity 1.2 Ah, respectively 14.4 Wh.

Battery packs are disassembled in different ways, but most often the case is twisted using several self-tapping screws. Although I came across options both with latches and glued.

In any case, inside you will see something like this. In this case, an assembly of 10 nickel-cadmium batteries is used, and batteries of the same standard size are usually used, but their placement may sometimes differ. The photo shows one of the common options, 9 pieces at the bottom and one in the vertical part.

The first thing to do is selection of replacement batteries.

Power tools use batteries designed for high discharge current.
Not long ago I made different batteries, at the end of which I provided a plate that can help in this matter, but if you are not sure, then just find the documentation for the batteries you are planning to buy. Fortunately, branded batteries usually have no problems with this.

It should be remembered that often the declared battery capacity is inversely proportional to the maximum current supplied. Those. The higher the current the battery is designed for, the less capacity it has. The example is of course quite conventional, but very close to reality. For example, very capacious Panasonic NCR18650B batteries are not suitable for power tools, since their maximum current is only 6.8 Amperes, while a screwdriver consumes 15-40 Amps.

Now what not to use:
The batteries shown in the photo below, as well as all sorts of Ultrafire, Megafire, as well as any 18650 with a stated capacity of 100500 mAh.
In addition, I categorically do not recommend using old batteries from laptop batteries. Firstly, they are not designed for such a current, and secondly, they will most likely have a wide range of characteristics. And not only in terms of capacity, but also in terms of internal resistance. It’s better to use them somewhere else, for example in the PowerBank to charge your smartphone.

An alternative option is model batteries, for example for boats, quadcopters, cars, etc.
It is quite possible to use, but I would prefer the usual 18650 or 26650 and the presence of a durable case, as well as a more realistic replacement in the future. 18650 and 26650 are easy to buy, but model ones can be removed from sale, replacing them with batteries of a different form factor.

But among other things, you should remember that you cannot use batteries of different capacities. In general, it is advisable to use batteries from one batch and buy the required quantity at once (ideally +1 in reserve, if you still come across different ones). Those. If you have 2 batteries lying on your shelf for a year, and then you buy a pair of new ones and connect them in series, then this is an extra chance of getting problems and balancing may not help here, not to mention batteries with initially different capacities.

To remake the battery of this screwdriver, LGDBHG21865 batteries were chosen.
The screwdriver is not very powerful, so I think there should be no problems. The batteries are designed for a long-term discharge current of 20 Amps; when choosing batteries, you should find the corresponding line in the documentation for the battery and see what current is indicated there.

Lithium batteries have a noticeably higher capacity with smaller dimensions than cadmium batteries. In the photo on the left is the assembly 10.8V 3Ah (32Wh), on the right is the original one, 12V 1.2Ah (14.4Wh).

When choosing the number of required batteries for replacement, you should be guided by the fact that one lithium battery (LiIon, LiPol) replaces 3 regular ones. A 12 Volt battery costs 10 pieces, so they are usually replaced with 3 lithium pieces. You can put 4 pieces, but the tool will work with overload and there may be situations where it may get damaged.
If you have an 18 Volt battery, then most likely there are 15 regular ones, which are replaced by 5 lithium ones, but such a tool is less common.
Or in simple terms,
2-3 NiCd = 1 lithium,
5-6-7 NiCd = 2 lithium,
8-9-10 NiCd = 3 lithium,
11-12-13 NiCd = 4 lithium
etc.

Before assembling, it is necessary to check the capacity of the batteries, because even in one batch the batteries may have a spread, and the more “unoriginal” the manufacturer, the greater the spread will be.
For example, a plate from one of mine, where I tested, and at the same time selected sets of batteries for converting radio stations.

After this, you should fully charge all batteries to equalize their charge.

Battery connection.
Several solutions are used to connect batteries:
1. Cassettes
2. Soldering
3. Spot welding.

1. Cassette, very simple and affordable, but categorically not recommended for high currents, as it has a high contact resistance.
2. Soldering. It has a right to life, I do it myself sometimes, but this method has nuances.
At the very least you need to know how to solder. Moreover, be able to solder correctly, and most importantly - quickly.
In addition, you must have an appropriate soldering iron.
Soldering occurs as follows: We clean the contact area, cover this area with flux (I use F3), take a tinned wire (preferably not a very large cross-section, 0.75mm.kv is enough), put a lot of solder on the soldering iron tip, touch the wire and with it press it to the battery contact. Or we apply the wire to the soldering area and use a soldering iron with a large drop of solder to touch the place between the wire and the battery.
But as I wrote above, the method has nuances; you need a powerful soldering iron with massive sting. The battery has a large heat capacity and with a light tip it will simply cool it down to such a temperature that the solder “freezes,” sometimes along with the tip (depending on the soldering iron). As a result, you will spend a long time trying to warm up the contact point and eventually overheat the battery.
Therefore, take an old soldering iron with a large copper tip, preferably well heated, then only the soldering area will warm up and after that the heat will simply be distributed and the overall temperature will not be very high.
The problems relate to the negative terminal of the battery; there are usually no difficulties with soldering the positive terminal, it is easier, but I also do not recommend overheating it too much.

In any case, if you do not have soldering experience, I highly do not recommend this method.

3. The most correct way is spot welding, instantly, without overheating. But the welding machine must be properly configured so as not to make a through hole in the bottom of the battery, so it is better to turn to professionals. For a little money, they will weld your battery for you at the market.
An alternative option, some online stores offer a service (or rather, lot options, with or without petals) for welding contact petals; this is not very expensive, but much safer than soldering.

This assembly was “welded” by the same friend who gave me the screwdriver for review.
The photo shows that a rag insulator is laid between the petal and the battery body. This is important, because without it you can overheat the petal and it will melt the battery insulation, I think the consequences are clear.

Attentive readers have probably noticed the strange plastic spacers between the batteries.
This solution belongs to the class - how to do it right.
The tool is subject to vibration in operation and the insulation between the banks may be damaged (I have not seen this, but theoretically). Installing spacers eliminates this situation. You don’t have to put it, but it’s more correct. I can’t tell you where to buy them, but you can look for them in battery kiosks.

Then you need to bring out the wires to connect to the protection board and terminal block.
For power wires I use a wire with a cross-section of at least 1.5mm.sq., and for less loaded circuits 0.5mm.sq.m.
Of course, you will ask why a 0.5 mm kV wire if there is no current and you can use a much thinner wire. Wire with a larger cross-section has thicker insulation and provides greater mechanical strength, i.e. it is more difficult to damage. Of course, you can use any wire, I just showed the option that I think is more correct.
Ideally, the wires should first be tinned on both sides and the free ends insulated, but this is possible during the second rework of the same battery, when the length of the wires is already known. For the first one, I usually take extra wires.

If you look closely, in the top photo you can see holes in the outer terminals of the battery; this is also done to improve the reliability of the connection. An untinned wire is inserted into the hole and sealed, in this case there is less risk of getting a bad contact.
In general, we solder the wires, at the same time it is advisable to additionally insulate the terminals using heat shrink.

As a result, we will end up with an assembly like this. Two wires come from the positive contact; this is due to the way the protection board is connected.

The last step in preparing the build is more desirable than required. Since the assembly is “live”, it is necessary to fix the elements relative to each other. For this I use heat shrink tubing, although in this case it would be more correct to use a pipe. It is quite thin, but very durable, its purpose is to compress the entire structure.

We put on the heat shrink and use a hairdryer to shrink it. The usual option with a lighter most likely will not work, since it is advisable to do it evenly.
In our toga we have a completely factory-like assembly of batteries.

Let's try on the assembled assembly in the case. In general, of course, they usually do this first, I somehow missed this point, but I think it’s quite logical :)

Installation.

Next comes the stage of installing the assembly into the battery compartment. A seemingly trivial operation hides small pitfalls.
First, wash away the dust and dirt from the compartment. I made a mistake and wiped only the lower part, then cleaned the rest with a brush and cotton wool. Therefore, it is easier to wash with soap and dry.

Next is gluing the assembly. In the original version, the batteries were simply clamped between the body halves, but in our case this is rarely possible, so the assemblies are most often glued.
Here, as before, there are several options, let's consider them.
1. Double-sided tape
2. Hot melt adhesive
3. Silicone sealant
4. Nail through with 150 nails and bend on the other side. :)

Since the last option is more suitable for extreme sports enthusiasts, I will describe the more “down-to-earth” ones.
1. It’s very simple and convenient, but since the contact point is small, it doesn’t hold very well, and besides, you need to use good tape.

2. This is a good option, I sometimes use it myself (by the way, I use black hot melt glue). But in this case I would not recommend it. The fact is that hot melt adhesive tends to “float” when heated. To do this, it’s enough to forget the screwdriver outside in the summer and end up with a battery dangling inside. I won’t say that this will necessarily happen, but glue has such a property, it’s a fact. In addition, hot-melt adhesive does not adhere very well to massive elements and may simply fall off under load.

3. In my opinion, the most convenient option. The sealant is not afraid of heat, does not flow over time and has good adhesion to most materials. In addition, it is quite elastic and practically does not lose elasticity over time.

I used Ceresit sanitary sealant. In the photo it may seem that it is barely smeared, this is not so, there is quite a lot of sealant. By the way, it should be borne in mind that most sealants do not adhere to the previous layer of sealant.
In addition, you can use similar mounting adhesive in the same tubes, for example “Moment”, but silicone seems to me more suitable.

In general, we apply sealant, insert our assembly, press it and leave it to dry.

Protection board.

Now we have come to the actual subject of this review, the protection board. They were ordered back in the spring, but the package was lost, they were then sent again, and in the end they finally arrived.
I don’t remember why these particular boards were ordered, but they lay quietly and waited in the wings, they waited :)

This board is designed to connect three batteries and has a stated operating current of 20 Amps.
Only now I noticed that the board has a fairly high threshold for overvoltage protection, 4.325 Volts. Maybe I'm wrong, but I think that 4.25-4.27 is better.
It is also indicated that the current of 20 Amperes is the maximum continuous current, the operating current during overload is 52 Amperes.

The plate is very similar to the plates from other boards, so I will highlight certain important points.
1. Balancing current, since this board cannot do this, there is a dash here
2. Maximum continuous current, for most applications you need 20-25 Amps. On a less powerful instrument, 15-20 is enough, a more powerful one will require 25-35 or more.
3. The maximum voltage on the element at which the board turns off the battery. Depends on the type of batteries used.
4. Minimum voltage on the element at which the board will turn off the load. 2.5 Volts is quite small, it is better to choose this parameter the same as stated in the datasheet for the battery.
5. Current at which overload protection is triggered. There is no need to strive for exorbitant values. Although this current is directly related to the maximum operating current, therefore there are usually no problems here. Even if the protection is triggered, most often it is enough to simply release the screwdriver button and then press it again.
6. This item is responsible for automatically resetting the protection.
7. Resistance of key transistors, the lower, the better.

Externally there are no complaints about the board; the build quality is quite neat.

There is nothing underneath, this is for the best, there will be no problems with gluing the board :)

I'll tell you a little more about protection boards.
First, I’ll answer the question: is it possible without a protection board? No.
At a minimum, the protection board provides a shutdown when overloaded; this is harmful to both the batteries and the tool.
In addition, the board protects against overcharge and overdischarge. In fact, we can say that overdischarge can be felt by a drop in power, but this does not apply to all instruments, and in addition, you can find yourself in a situation where one element is very “tired” and the voltage on it drops very sharply. In this embodiment, it is easy to obtain a polarity reversal, i.e. The battery will not just go to “zero”, but current will flow through it in reverse polarity. This effect is obtained only when the elements are connected in series, and for some reason it is often forgotten.
Lithium batteries are quite dangerous and a protection board is required for them!

Boards are mainly divided into two types (although in fact there are more of them), with and without balancing capabilities.

I will explain what balancing is and why it is needed at all.
First, the “passive” balancing option.
This option is used on the vast majority of boards as the easiest to implement.
As the battery reaches the threshold voltage, it begins to load on the resistor, which takes on part of the charging current. While this battery is “struggling”, others manage to charge to their maximum.
Below are a few pictures from this one.

1. One of the batteries is either more charged than the others or has a slightly lower capacity.
2. In the case of a simple charge, the voltage on it will be higher than on the others
3. The balancer absorbs part of the charge current, preventing the voltage from rising above the maximum.
4. As a result, all batteries are charged evenly.

In addition, I talked a little about balancers in a separate video.

The second version of the balancer, “active”. It has a completely different implementation and is not suitable for working with high charge currents. Its task is to always maintain the same voltage across the elements. It works on the principle of “pumping” energy from a battery with a higher voltage to a battery with a lower voltage. In one of my own, I made such a balancer; anyone interested can read it in a little more detail.
And in this one I did a variant of correct charging with an active balancer and from there a sign where you can see the balancing process without connecting the battery and the board to the charger... Yes, it is slow, but it always happens, and not just during charging.

We got a little distracted.
A balanced protection board usually contains several large SMD resistors, the number of which is a multiple of the number of channels. with 3 channels it is 3 or 6. Most often they say something like 470, 510, 101, etc.
The board has 4 channels on the left, 3 channels on the right.

There is no balancer here, but there are current-measuring shunts in the form of SMD resistors with low resistance. They usually say R010, R005. Therefore, a board with and without a balancer can be distinguished by its appearance.
By the way, the boards may not have a current-measuring shunt. This does not always mean that the board cannot measure current. It’s just that sometimes the controller knows how to use field-effect transistors as a “shunt”.

There are also separate balancer boards, as well as balancer + protection board kits.
This option has a right to life if the price suits you, but there will be more wires.

Along the way, I often come across misconceptions about the possibility of using these boards as a charger. People are usually confused by the word Charge in the lot listing.
These boards cannot control charge, they only protect batteries. But the illiteracy of sellers or crooked translation takes its toll and people continue to make mistakes.
But there are also “all-in-one” boards, although they are not designed for high currents and are not suitable for power tools.

This board has eight key transistors, or rather four pairs.
Transistors are used and they accordingly have a resistance and maximum current - 5.9 mOhm 46 Amperes and 4 mOhm 85 Amperes.
The current measuring shunt is visible on the left. This option is more preferable than SMD resistors, which sometimes tend to “burn” due to high pulse currents.

The board does not have a central controller and is assembled using a rather primitive circuit design, channel voltage monitors and then a circuit that reduces everything to controlling field-effect transistors. It's simple, but it works. Although now I would probably choose something more “advanced”.
In addition, the board does not have a balancer. You may ask how this is, because I described the advantages of a balancer above.
The balancer is good, and I recommend buying boards with it. But I also believe that normally selected batteries do not really need a balancer; it will not save you from a strong fall, but can add problems. There have been cases when a faulty balancer drained the battery.
In addition, most power tool manufacturers do not include balancers in their battery packs. True, the principle of “planned obsolescence” applies there, so I’m still more for the balancer than against it.

In addition, the board has contacts for connecting a temperature sensor (and above in the photo from another store there is an example of such a board with a temperature sensor). The thermal sensor is good and my plans are to figure out how to connect the native thermal sensor of the screwdriver battery.
Presumably, you need to unsolder the RT resistor, replace the RY resistor with a value corresponding to the value of the new sensor, and solder the new sensor to the RK contacts.

We seem to have sorted out the boards a little, let's move on to continuing the rework.

Since the board can heat up during operation (although not much), I decided to make a gasket to protect the batteries from excess heat. In addition, it will protect the batteries in the event of a rupture of field-effect transistors and a burnout of the board (this happens, but extremely rarely, so it’s more theoretical).
I took a piece of fiberglass and removed the foil.

Then, using the same silicone sealant, I glued the gasket to the battery assembly, and then glued the board itself.
The design is certainly terrible, but in this case it is the simplest and fairly reliable solution.
The board was not glued “by chance”; first I figured out how it would be more convenient to connect it later.

The connection diagram was on the store page, but in reality it is practically no different from the connection diagrams of other boards. The batteries are in series, minus to the board, the first midpoint counting from minus is B1+, the second is B2+, the third is B3+. But since there are only three batteries, B3+ is a plus for the whole assembly.
The second wire from the positive terminal goes to the load.
The negative wire of the load (as well as the charger) is connected to a separate contact of the board.

Next we connect the wires.
The order in which the wires are connected can be critical; I usually connect the negative assembly first, then the positive, and only then the middle points starting from the negative terminal (B1, B2, etc.).
There is information that an incorrect connection sequence can burn out the controller, I wanted to add it to the review, but did not find any links.
In addition, you need to solder very carefully so as not to short-circuit the contacts, otherwise there will be a sad picture. This is perhaps one of the most difficult stages in reworking for a beginner... I first tin the board pads and then solder, it’s easier that way.

Ideally, the wires should also be secured with sealant so that they do not dangle.

At the very beginning, I showed the battery pack that I removed from the battery compartment.
The terminal block is visible from above; you cannot throw it away, as it is very important for the rework. The terminal blocks are different, but they have the same essence, a quick connection to a tool or charger.
At first, when I started remaking, I decided that the resistor here sets the charging voltage (the charger is designed for 7.2-14.4 Volts), but a check showed that the charger does not even have a corresponding contact for it, just like the screwdriver :(
A thermistor is connected to another of the contacts to monitor the temperature of the battery, although this did not help much; one of the battery blocks has obvious signs of overheating and deformed plastic.

But before connecting, you should think about fixing the terminal block. Initially, it was held by batteries, but since there are no batteries anymore, you will have to improvise.
To secure it, I measured the inside width of the protruding part and then cut a piece of plastic to the appropriate width. True, I still made a little mistake and cut out a little less, I had to wrap some electrical tape :)

Usually both wires are unsoldered, but in my case the negative wire was of sufficient length and I did not remove it, but replaced only the positive one.
By the way, since the terminal block is made of plastic, and the terminals themselves are quite massive, here we either use the same principle as when soldering batteries, or simply bite off the old wire 7-10mm from the end of the terminal and solder a new wire to it. The second option is no worse, but noticeably simpler.

1. Solder the positive wire of the assembly to the terminal block. Heat shrinking is more of a perfectionism, there’s really nowhere to shorten it, but I wanted to do it carefully.
2. We insert the terminal block into its original place, hammer in (or press very hard) the plastic retainer that I cut out above.

We solder the negative wire from the terminal block to the board and cover the board with protective varnish. But the latter is no longer perfectionism, but quite useful, since the board is under voltage and can be used in conditions of high humidity. If you do not varnish the board, corrosion of the exposed parts of the traces and component leads is possible.
I use Plastic 70 varnish.

That's all with the battery, put back the springs, clamps and put them back together.
First, it is better to turn the entire structure over and shake out anything that could accidentally get inside; for me it was a piece of wire insulation.
At the same time, you can wipe/lubricate the battery fixing mechanism in the screwdriver.

The minimum program has been completed, the battery is working, but since the original charger has not yet been converted, I connected it to the power supply for now.

Since reworking the charger (and more) will most likely not fit into this review, and I want to do it beautifully and correctly, another review on this topic is planned, where I will talk about possible modifications, reworking the charger and options correct charge.

For charging, you can of course use a common Imax type charger. But I find this option inconvenient.
In addition, sometimes a connector is provided for balancing screwdriver batteries. The thing is certainly useful, but as for me, it’s a little unnecessary, and besides, it’s not always safe. In my opinion, it is enough to simply select the batteries once and then simply charge without balancing. Or buy a protection board with a balancer, and protruding connectors increase the chance of them being shorted or broken, and this is more of an option for home use.

For a more realistic application, it is better to either remake the original charger or completely replace its “filling”.
The first option is technically complex, since the charging algorithm for a lithium battery is noticeably different from that of a cadmium battery, and besides, some native chargers are hard to call; inside there is only a transformer, a diode bridge and a bunch of parts, there is no trace of any control.
For example, Bosch also has an “advanced” version, with a controller.

As a second option, you can use the charger’s original transformer, its diode bridge and a piece of printed circuit board as a terminal block.

To remake it, you need to buy an additional board like the one in the photo.
Or any other that can stabilize voltage and current. Typically these boards have at least two trim resistors. But in this case there are even three, the third regulates the threshold for turning on the end of charge indication.

If you look at the photo, the first is voltage, the second is indication, the third is charge current.

In this option, the board is connected instead of the original one; you will only have to add an electrolytic capacitor with a capacity of 1000-2200 μF.

But this solution also has its downsides. The charger board only displays the completion of the charging process, but does not disconnect the battery. It’s not that it’s completely bad, it’s bad, but there’s nothing good about it either.
To solve this problem, you can use the simplest solution: turn off the output after the charging process is completed.
To do this, you will have to add four parts, a 24 Volt relay, a PC817 optocoupler, a diode and a button.
The optocoupler LED turns on instead of the LED indicating the charging process, and the optocoupler transistor controls the relay.
But in this version, the relay cannot turn on itself, therefore a button is needed parallel to the contacts (as I said, the solution is very simple). Those. inserted the battery, pressed the button, the charging process began, after the charging was completed, the relay turned off and the battery was de-energized.
The button can be connected parallel to the contacts of the optocoupler transistor, then a regular clock button will do. Naturally, in both cases you need a non-latching button.

Optocoupler and relay.

You can also use other boards; many have probably seen them on Ali.
The first is simpler, only the current and voltage are regulated, the charge indication is set fixed, the LED goes out when the current drops less than 1/10 of the set charge current (standard lithium charging algorithm).
The second is essentially like the first, but in a more “advanced” version, the battery voltage and its charging current are displayed.
Review, and.

By the way, you can even use a board without current stabilization for charging, but you will have to modify it a little, I even showed it.

All of the above options use the charger’s native transformer, but if it is not there, then the converter simply needs to be supplemented with a power supply, for example this one.
but it’s worth considering that the power supply must be a voltage higher than the end-of-charge voltage of the battery, the difference needs to be about 3-5 Volts or more.
Those. in this case, a 15 Volt power supply is not suitable, but usually such power supplies have output voltage adjustments of ±20% and it can be raised slightly. But you can just buy a 24 Volt power supply and not adjust anything.

If you only have a 12-volt power supply, but you need to charge the battery as in the review, then you can use a universal converter, for example, although it costs more.

About improvements.
You can add a battery charge indication, such as sound or sound + light.

Either measure the voltage using a small one, or even install a hybrid voltmeter + sound.

But personally, I prefer simple options, voltage measurement with indication by several LEDs.

Moreover, I already made the last version, both the design and production.

Almost the same option is used in one of my batteries, or rather in its batteries.

A short video of the result of the alteration. The video shows that in severe cases the protection is triggered. The battery was already a little low, so in ratchet mode at second speed the protection did not always work. This happens more often when the battery is fully charged. But it is also clear that the protection is triggered correctly, load, shutdown. After that, I release the button, press it again and the screwdriver works.

For greater convenience, you can use the plastic frames that I showed in my videos.

To charge, use a similar charger.

That’s all in general terms, about remaking the batteries I told him everything I remembered, but about the charger I’ll tell you in more detail some other time, since I have a lot of ideas.

Yes, I almost forgot about the actual subject of the review, the protection board.
The board works, works great, at least I didn't find any problems with it.
When you clamp the chuck, set the ratchet to maximum (like level 5) and the second speed, the board goes into protection with about a 50/50 chance. If you turn on the first speed, there is not enough current to trigger the protection. In general, quite normal behavior. You can reduce the value of the shunt and the protection will work later, but I don’t see the point in this.

Yes, now about the cost of the rework. The price of three batteries is about 15 dollars + 5-8 protection board + a dollar for all sorts of small things, in total it comes out to about 20-25 dollars for one battery.
Expensive? I think it’s quite expensive, so there’s simply no point in remaking a cheap instrument. But in any case, the alteration is not as difficult as it seems at first glance, the main thing is to start.

In the review I did not write about LiFe batteries; by and large, everything is absolutely the same with them, except that they require special boards, since the voltage of these batteries is slightly lower than that of conventional LiIon. The batteries are excellent, the reliability with them will be higher, but the battery capacity will be lower.

I hope that the review was useful, as always, I welcome questions in the comments.
Naturally, options are possible, and I could also be wrong somewhere, so the above is only my vision of the process.