This review will briefly examine the high-current protection board for Li-Ion batteries, the non-standard use of a USB tester, a current-limiting step-down converter, and modifications to the standard Makita charger.
I have no desire to change the shurik, it suits me. The price of a new original PA 12 battery reaches 2-2.5 thousand rubles. That's why I decided to bother with the alteration. But not anyhow, but wisely.
If interested, look further.
Heroes of the story:
1. Makita 6271D screwdriver. Which has served me faithfully for more than 7 years.
Naturally, the original batteries died, and I always had a complaint about them.
Almost everyone who has worked with them knows about the disadvantages of Ni-Cd batteries. Requires careful charge-discharge relationship, high self-discharge, weight.
2. 3S 30A BMS PCM li-ion protection board.
Purchase price: 684 rub. 
1) Over-charge protection voltage with single cell:4.25V±0.025V
2) Over-discharge protection voltage with single cell:2.50±0.1V
3)Max continuous working current:30A
4) Over-current protection:40A
5) Suggest charge current: 1A-2A
6) Functions: Over-charge protection, over-discharge protection,
over-current protection ,short circuit protection .High temperature detecting protection
6) Size:43*37mm
Seller's warning:
3.Use 12.6V li-ion charger, don't use too high voltage charger OR high current charger to charge it.
Prices are in rubles, why?
I live in Russia, this resource is located in the Russian zone, I earn in rubles, on the card in rubles, I pay for goods in rubles. I see no point in converting into another currency. The seller's prices may change, there may be promotions, etc. I specifically indicated links to the store, go there and set the price even in tubes, the store will recalculate it itself. DEL
The total cost of the rework was (battery + charger) ~ 2"700 rubles.
The main parameters that I determined for myself:
1. A good board for at least 30A with balancing, the dimensions should fit into the dimensions of a standard battery.
2. High-current batteries of at least 20A, with a capacity of at least 2Ah.
3. Charge control, volt-amperes. Considering the size and functionality, the JUWEI J7-t simply has no competitors. Current up to 5A, voltage up to 30V, temperature sensor on board. While in stock it has little functionality, in my case it is in great demand.
The biggest problems arose with the board. All the boards that I liked did not fit into the dimensions, maximum 35*65mm. Initially I looked at 4 bank ones.
I decided to buy 3 banks and a separate balancing board.
Battery conversion.
The easiest thing was to remake the battery itself. This is done simply, tap the perimeter of the seam with a rubber hammer and it is divided into two halves. No damage or dancing with a knife. 
We throw out the dead cans, here you need to tinker a little. The assembly is filled with glue to the bottom of the battery.
Just in case, I left the standard thermocouple, although there is no point in using it now. And I transferred the protective fuse from the negative contact of the battery to the charging input of the board. 
If you look at it, the standard battery is charged through a separate contact, in addition to the load contact.
Fee in the amount: 
There is no spot welding, I plan to do it in the near future, while the parts are on the way...
I took a 100 watt soldering iron and quickly soldered the wires, the thermal effect was minimal. 
I know that this is not right and that it cannot be done. But I am a person far from science and put a jade rod on this complexity.
Next, I connected all the wires according to the instructions. 
I glued the thermal fuses to the batteries using Kafuter K-5204K thermal conductive glue 
The balancing board has not arrived yet, I will connect it later, as described in the example on the product page: 
Arrived, finished: 
That's all, a freebie.
P.S. “freebie” - in the sense of the complexity of the rework, not the price. 
As a result, a significant decrease in weight. Original weight 668 grams, for Li-Ion ~250 grams. Capacity 2.5Ah versus 1.3Ah for the original. In general, all indicators have doubled.
The issue price is ~1840 rubles (battery only) lower than the original.
PA12 battery after many years of life
I decided to check the low voltage cut-off using a highly intelligent 55-watt “Svetoch” discharge. 
At a voltage of 7.6V, the current supply is turned off. All is good.
Charger upgrade.
Here's a little dance with a tambourine. The task is to completely preserve the native functionality. And add the ability to charge converted batteries.
Problem number one, location! He is sorely lacking. The layout turned out to be very tight. And it caused problem number two, heating. But first things first.
I took two probes and started moving them around the board looking for suitable voltages. It was found at the output of the transformer at 55V~ Next there was a diode, the output of which was already 27V, which is what was needed. One contact was made through the power button. I installed an additional diode bridge and placed it on a standard radiator through heat-conducting glue. Added a 50v 1000uF capacitor. And after that I applied it to a step-down converter. Standard charging is based on minus, but for me it works on the basis of plus. I installed 3 relays that will switch different charging methods. I glued a white LED next to the standard indicators as an indication of operation for Li-ion. In Li-ion charging mode, 3 wires are discarded, two are connected to the output of the converter.
I placed a USB tester between the battery holder and the charging boards.
I unsoldered the connectors to reduce the size and divided them into two halves. The screen and board are 90" each, due to the peculiarities of the internal placement.
I took a knife and started cutting out the plastic in the case. 
Before installation, I checked the tester parameters. I set it to 30 and connected a 55 watt light bulb (12V). The flight is normal, it holds 30V. 
And then I accidentally touched the output contacts on the short circuit. As you know, all radio components operate on white smoke. The output mosfet AO3415 emitted white smoke and went into another world.
I went to the local shamans, they gave me an amulet AO3401 that was similar in terms of performance characteristics, demanding 43 rubles for its soul, I took 2 pieces;) When I returned, I moved the bucket closer and replaced the amulet, everything worked perfectly.
I set the operating time to 2 hours. Press the button five times in a row and set the desired value. I haven’t checked it yet, but in theory it should start beeping.
The next hit on the tambourine is associated with the settings of the converter itself. At idle we get a current consumption of 0.21A. these are 3 relays. Initially, I connected the tester incorrectly, immediately after the step-down voltage converter (hereinafter referred to as PPN). Why do we also need to count the energy spent on the operation of the relay, I redid it. 
According to the battery datasheet, the standard charge current is 1.5A, and this is what was set on the PPN in CC mode.
With the tension I had to do some magic. Initially I set it to 14.4V in case I mixed up the batteries, so that they would charge in any case. But the test showed a strange picture.
The current consumption is stable at a maximum of 1.5A As soon as a voltage of 12.75V (4.25 per 1) appears on the batteries. charging stops immediately. In this mode, the transferred capacity is 2200 mAh. something is not enough.
More correct charging and a smooth reduction in current consumption towards the end of the charge were achieved with a voltage of 13.43 V at the input to the protection board. The shutdown occurred at a current of 0.12A and a voltage of 12.76V. on batteries. For high current ones this parameter is 100-150mA. 
Video of charging process 1.5A
Broken into two parts, they called the phone.
Temperature measurements.
Heating with an open case was up to 70" on the transistor, inductor and diode bridge.
A small radiator was installed on the PPN, and the diode bridge was glued to the standard one.
There was absolutely no space left inside the case. When the case is closed, the temperature will be significantly higher. I assembled it and started testing. After 10 minutes, a click sounded and another soul left the memory. Having opened the case, I saw a crack in the XL4005, about a bucket nearby. It's good that I order almost everything in twos. 
I decided to install an external cooling fan.
In Pandora's box I found an old video card with a suitable fan, I still need to install a protective grille, I didn't have it at hand.
The temperature dropped significantly, to approximately 32" across all elements.
Against this background, I decided to increase the current; according to the datasheet, up to 4A is allowed, so I set it to 2A.
2A charging process video
You can see how the protection works. There may be several reasons, the current exceeding 2A, the voltage on one of the elements becomes more than 4.25V, overheating.
I didn't notice the product description right away: 5) Suggest charge current: 1A-2A
Gaining 80% capacity, 2,000mAh occurs in an hour.
The layout is dense, placed with millimeter precision, standard parts are not affected.
Let's compare before and after the alteration. 
There are exit holes on the opposite side and three if I accidentally put it on a soft surface and the main ones will overlap. 
General connection diagram: 
Current cutoff test.
At second speed it works quickly.
I couldn’t hold on to the first one, it turns.
After thinking a little, I set the final characteristics on the PPN based on the characteristics on the memory connector: CC=1.9A CV=13.38v
I didn’t record a video, it takes too much time. And most importantly, the phone is lying there and cannot be touched while the recording is in progress. The overall picture is already clear. Shutdown should occur at 80-110mA. By reducing or removing protection triggers. Charging time approximately 1:45:00
Let's summarize. 
Everything works as intended.
I don’t see any obvious disadvantages, only the fan is noisy.
-Full charging time is about two hours.
Pros:
-Significant weight loss.
-Increasing capacity.
-A capacity of 1"250mAh (50%) takes 35 minutes, which is comparable in time and capacity to a standard battery.
-Charge control with capacity calculation.
-Two battery charging modes, native Ni-Cd & Ni-Mh and new Li-Ion.
-Experience.
If you find any errors anywhere, write in a personal message or in the comments.
Any recommendations for improvement are also welcome.
Properties
Description
From us you can buy a charge-discharge controller (PCM) for Li-Pol, Li-Ion battery 3.7V 28x4mm 2pin 265-sxt-2845 JWT at a price of 135 rubles. with the possibility of ordering installation and repair services. You can pay for the purchase of a charge-discharge controller (PCM) for Li-Pol, Li-Ion batteries 3.7V 28x4mm 2pin 265-sxt-2845 JWT in cash, electronic money, bank card, bank account, cash on delivery or by bank transfer. It is possible to deliver the goods using our courier services in Moscow, using a courier company or by Russian Post. In addition, a pick-up point in Moscow is at your service.
On the website "Magazin-Details.RU" you can quickly order and buy a Charge-Discharge Controller (PCM) for Li-Pol, Li-Ion batteries 3.7V 28x4mm 2pin 265-sxt-2845 JWT. The price for the presented product is one of the most attractive, and we offer high-quality components that we supply directly from factories. This scheme of work will allow us not to include the services of intermediaries and resellers in the price. You can find out how much a Charge-Discharge Controller (PCM) for Li-Pol, Li-Ion batteries 3.7V 28x4mm 2pin 265-sxt-2845 JWT Universal costs through the website or by calling our managers. Here you will receive high-quality service and reliable components, which is confirmed by reviews from our regular customers. We are ready to promptly answer all technical questions, help you formulate an application and select the optimal solution. Our company has been engaged in remote sales for several years and our specialists are ready to solve any task. We deliver orders throughout Russia. For residents of the capital, goods are usually delivered the next business day, it is also possible to receive the purchase the same day and a pick-up service is available. Purchases are delivered across regions by trusted transport companies. The receipt period can take up to two weeks, it depends on the remoteness of the locality and the tariff.
1) Delivery by courier in Moscow.Carried out by our online store’s own couriers. To use delivery, you must select this method of receiving your order when making a purchase. Delivery is usually carried out on the next business day after placing the order (if a courier is available, delivery can be carried out on the same day).
The cost of delivery in Moscow (within the Moscow Ring Road) is:
319 rubles for goods with a total value of up to 1000 rubles;
279 rubles for goods with a total value of up to 3,000 rubles
249 rubles for goods with a total value from 3,000 to 12,000 rubles;
The cost of delivery in Moscow (outside the Moscow Ring Road) is:
350 rubles for goods with a total value of up to 1000 rubles;
300 rubles for goods with a total value of 1,000 to 12,000 rubles;
For goods costing over 12,000 rubles, delivery within Moscow is free.
2)Receipt of goods at company offices. If you have chosen this method of receiving the goods, after registration, wait for a call from the manager to confirm the availability and reservation of the goods in the warehouse. You can also reserve goods for pickup by phone.
3)Sending through a courier company. You can order delivery from any of the courier companies presented on the website. Delivery is carried out to the recipient's address or to the delivery points of courier companies.
The exact delivery time and cost depend on the choice of courier service, the weight and volume characteristics of the order and the distance to the delivery point. Delivery time and cost are calculated automatically in the shopping cart when placing an order.
4)Sending by Russian Post. Carried out according to the post office code and recipient's address. Post restante shipments are made only upon prepayment.
You can pay for your purchase in the following ways:
1) Cash upon receipt at the company office or by courier delivery.
2) Electronic money on the site - Yandex.Money, WebMoney (service operator - Yandex company), Qiwi (by wallet number after agreement with the manager).
3) By bank card on the website (service operator - Yandex company).
4) By bank account (you can pay the bill at the bank or through a client bank).
5) Cash on delivery when sending to the regions. Payment is made to the courier company. No prepayment required.
How to pay for an order for legal entities?
1) For non-cash payment You must issue an invoice by selecting the appropriate payment type during checkout. After issuing an invoice for the product you have chosen, it is reserved for 5 banking days, including the day the invoice is issued. The goods are shipped only after receipt of 100% advance payment for the order to the company's bank account. Upon shipment, we will provide you with the entire set of documents (please note, we work without VAT).
2) Pay for your order in cash(purchase is made to the organization) . Please note that in this case you must have a power of attorney to receive goods from Tekhnomir LLC, or a seal of the organization. When making a purchase, you will be given a complete set of shipping accounting documents (please note: we work without VAT).
Product warranty
We strive to resolve any problem with a product purchased in our store as quickly as possible.
In the event of a defect in any purchased product, we undertake to exchange it or return the full price paid for it during the entire warranty period.
The following warranty periods for products apply in our store (unless these periods are indicated directly on the website of a specific product):
Matrices, screens, covers assembled with a matrix, displays, touchscreens, touchscreens assembled with a matrix, inverters, microcircuits, coolers, cables - 3 months from the date of receipt of the goods.
Batteries, power supplies, storage devices, RAM, drives- 3 months from the date of receipt.
Cables and accessories, connectors, consumables- no guarantee.
Return of goods of good quality within 14 (30**) days not counting the day of receipt (including those purchased by mistake)
Any buyer who purchased a product in our store has the right to return or exchange a product of good quality without traces of installation and use within 14 (30**) days after receiving it (for regional buyers, it is important to send the item back by carrier within 14 (30**) days after receiving it). In this case, the product will be replaced with a similar one or 100% of the amount paid for the product will be refunded. Delivery costs, as well as commission in case of cash on delivery, are additional services and are not included in the warranty! Re-sending the desired item will cost an additional fee.
**applies to products from sections " Touchscreens (sensors) for tablets and smartphones" And " Matrix + sensor modules for tablets and smartphones" due to the need to test them before installation in the device.
To return an item you must:
Return of faulty (defective) goods in case of detection of a defect during the entire warranty period
Any customer has the right to exchange defective goods during the entire warranty period, in this case:
1) the client has the right to receive the full cost of the goods, including the cost of delivery and the amount of cash on delivery, if he wants to return the goods.
2) in case of replacement of goods, delivery of goods (both from the client and to the client) is carried out at our expense.
To exchange goods you need:
Report the shipment details to the manager (full name, shipping method, invoice number, date, etc.)
Provide a copy or original of the invoice confirming the purchase of the goods, a warranty card (or a copy).
Deliver the goods to our office (Moscow) or ensure the goods are sent to our address from Russia (the method of delivery of the returned goods is agreed with our manager!)
Refunds for goods are made in a way convenient for you and for us after receiving the goods in agreement with our manager.
Note! The method of returning goods from Russia is agreed with our managers.
Voltage control on each cell:
When the voltage on any of the cells exceeds the threshold values, the entire battery is automatically turned off.
Current control:
When the load current exceeds threshold values, the entire battery is automatically turned off.
Description of pins:
"B-"- general battery minus
"B1"- +3.7V
"B2"- +7.4V
"B3"- +11.1V
"B+"- general battery plus
"P-"- minus load (charger)
"P+"- plus load (charger)
"T"- NTC 10K thermistor output
Controller: S-8254A
Datasheet for S-8254A.
Specifications
Model: 4S-EBD01-4.
Number of series-connected Li-Ion batteries: 4 pcs.
Operating voltages: 11.2V... 16.8V.
Cell overcharge voltage (VCU): 4.275±0.025V.
Overdischarge voltage (VDD): 2.3±0.1V.
Rated operating current: 3A - 4A.
Threshold current (IEC): 4A - 6A.
Overcharge protection.
Overdischarge protection.
Short circuit protection.
Dimensions, mm: 15 x 46.1 x 2.62.
Weight: 2 gr.
Guarantee
Every product we sell comes with a warranty. We always meet the client halfway and try to resolve all controversial situations. For more details, you can read the terms of exchange and return in our store by following the link.PCM is suitable for Li-Ion/Li-Pol. PCM is designed to protect against overcharge and deep discharge of 1...4 batteries.
In most modern portable devices, such as tablet computers, GPS navigators, e-readers, portable game consoles, solar energy storage devices, manufacturers use unpackaged lithium-polymer batteries. The main advantages of Li-Pol batteries are their small size with an acceptable battery capacity, the ability to be manufactured for a specific device, without resorting to established standards.
It is safe to say that lithium-polymer batteries are the most “delicate” batteries in existence, that is, they require mandatory compliance with several simple but mandatory rules, due to non-compliance with which either a fire occurs or the battery “dies”.
We list them in descending order of danger:
Charge to a voltage exceeding 4.2 V per cell;
Battery short circuit;
Discharge with currents exceeding the load capacity or heating the battery above 60 °C;
Discharge below voltage 3 V per cell;
Battery heating above 60˚C;
Battery depressurization;
Storage in a discharged state.
Failure to comply with the first three points leads to a fire, all others - to complete or partial loss of capacity.
Therefore, before installation in any gadget, each open-frame battery is equipped with a controller that protects the battery from overcharging and overdischarging, controls charging and discharging currents and voltages, which significantly extends the battery life and helps ensure safety.
The controller collects and processes information related to batteries and, using transistor switches, disconnects batteries from power. Resistors and capacitors provide external synchronization.
Provided that the charge and discharge voltages of the batteries correspond to the norm, there is no short circuit on the battery and its capacity has not reached its maximum, the transistor switches are open and the batteries can be freely charged and discharged.
If one of the specified parameters deviates from the norm, the controller supplies a closing voltage to the transistor switches. The voltage through the high resistance of the closed transistors is not supplied to the terminals of the batteries, which is why charging or discharging the batteries stops until all the necessary conditions meet the norm.
To avoid imbalance of batteries in a Li-Pol battery, the batteries are charged separately. For this purpose, the 4SBLi-7A5021 controller is used, which has 4 separate circuits, therefore it can charge a battery of four lithium batteries.
Connection diagram:
And again a device for homemade ones.
The module allows you to charge Li-Ion batteries (both protected and unprotected) from a USB port using a miniUSB cable.
The printed circuit board is double-sided fiberglass with metallization, the installation is neat. 
Charging is assembled on the basis of a specialized charge controller TP4056.
Real scheme. 
On the battery side, the device does not consume anything and can be left constantly connected to the battery. Short circuit protection at the output - yes (with current limitation 110mA). There is no protection against battery reverse polarity.
The miniUSB power supply is duplicated by nickels on the board. 
The device works like this:
When connecting power without a battery, the red LED lights up and the blue LED blinks periodically.
When you connect a discharged battery, the red LED goes out and the blue LED lights up - the charging process begins. As long as the battery voltage is less than 2.9V, the charging current is limited to 90-100mA. With an increase in voltage above 2.9V, the charge current sharply increases to 800mA with a further smooth increase to a nominal 1000mA.
When the voltage reaches 4.1V, the charging current begins to gradually decrease, then the voltage stabilizes at 4.2V and after the charging current decreases to 105mA, the LEDs begin to switch periodically, indicating the end of the charge, while the charge still continues by switching to the blue LED . Switching occurs in accordance with the hysteresis of the battery voltage control.
The nominal charge current is set by a 1.2 kOhm resistor. If necessary, the current can be reduced by increasing the resistor value according to the controller specification.
R (kOhm) - I (mA)
10 - 130
5 - 250
4 - 300
3 - 400
2 - 580
1.66 - 690
1.5 - 780
1.33 - 900
1.2 - 1000
The final charge voltage is hard-set at 4.2V - i.e. Not every battery will be 100% charged.
Controller specification.
Conclusion: The device is simple and useful for a specific task.
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