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I bought a Biswaye P103 (Chinese) battery to power my Ryobi drill, but when I tried to charge it using my bench power supply, it wouldn't work.
I did a teardown on the battery and a (borrowed) charger and found out how to bypass the Battery Management System (BMS).


Warning: Using the following could bypass the thermal and electrical protection circuits. Use at your own risk: I suggest the following:
Maximum of 21 volts (better is 20.5) for a 5-cell battery

Maximum current of AH / 4 is safe, more might be possible if you know the battery specifications
Charge in a fireproof container and don't charge unattended.


The battery has 4 terminals -

+ and - on the battery stem sides
T1 on the middle of the stem

T2 on the body of the battery.


Battery teardown:
Lots of pictures and information on the web so I won't repeat. I couldn't trace the number of the IC.


Charger teardown:
Ryobi P118B charger 140350004 FL19033D107838

Two 3-lead semiconductors, I presume they are MOSFETs. Number is 84312M 956BGH
One 20-lead IC. I couldn't read the numbers well, my best guess is 10266A J1A4B


Charger no-load voltages:
- to + 0.0
- to T1 5.0
- to T2 5.0


Voltages with a half-charged battery inserted:
- to + 19.96
- to T1 2.26
- to T2 1.61


The battery continued to charge when T2 was disconnected, but the light on the charger was red.


Terminal T1 battery characteristics:
Resistance approximately 7900 ohms. It was linear from 0.5 to 2.0 volts suggesting a pure resistance.
When the voltage was 0.5v or higher, the main +/- "opened" and it was possible to charge the battery. I suggest applying between 1 and 2 volts. Might want to put a ~4.7 K resistor in series for protection.


I presume the internal battery circuits will take care of cell balancing, but I suggest checking the individual cell voltages periodically.


Hope this helps.


Keywords: Ryobi lithium One+ One + BMS
 

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i don't know if the battery internals are the same as Ryobi, but i have dismantled both the 18 and 40V versions to trace the schematics and here is what i have found. https://www.diyelectriccar.com/forums/showpost.php?p=1011217&postcount=2


T1 is a Test terminal that is used by the charger to determine if the pack is okay—if the FETs are off then the pack will fail this test and the charger blinks the defective led pattern. The FETs connect the terminal labelled (-) to the bottom of cell 1.

T2 is a Test terminal with the same external indicator circuit as T1 for the state of the FETs, but it also has an internal indicator path to the PIC controller.

If anyone knows how to download and disassemble the firmware from a PIC16F1786, then we could look at the source code and get some ideas of what ryobi is doing.

The BMS chip on the ryobi board is an O2 micro, OZ8940ATN, which controls the FETs and also has a permanent failure mode to disable and drain a pack.
 

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Just found this thread. I've been rebuilding ryobi packs for a few months now and have found alot of strange things. Funny you mentioned getting the code off of the onboard pic. I'll be attempting it this weekend. not sure if I'll find anything as most of the time, the firmware is locked down.

Reviving these batteries is so painful and only works a fraction of the time (despite the cells being in excellent shape). getting the boards off of the batteries is a pain. I'm nearly to the point of attempting to spoof the signal lines needed to allow the ryobi charger to charge the battery, so that I can then use any 10s BMS instead of the junk ryobi has designed. If I make any headway, I'll update.
 

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Interesting event last night.

I rebuilt some 18v (P107) last week. I disassembled the pack, recharged/tested/recharged the cells (all still had great capacity). Reassembled, and still a number of the batteries failed to work. As mentioned previously, if the FETs are off, the Batt- and GND do not connect, no current will flow.

Last night while comparing a repair and functioning battery, to a repair and failed battery, the failed battery came back to life after taking a few voltage measurements and using the continuity checker on the FETs. I'm not exactly sure how this occurred, but I'll be trying to figure that out tonight.

I will say that failed 18v packs usually have just 1 cell that is damaged if any. I recently picked up 100+ 18v batteries that all "failed". After going thru about 30 of them, I've noticed that the previous owner had already tried jumping the batteries which involves bypassing the BMS. After measuring individual cell voltages, there is a massive difference in cell voltages. This can lead to a battery pack showing 16v, but only 4 of the cells actually working and hence, very likely, the FETs being off.
 

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i have found that in some cases i could charge individual cells (if lower than the rest) and get the FETs to come back on. Once the FETs revive, then the pack can be charged and used as normal in the tools.

The BMS is always ON and will drain a pack over time, so if it is seldom used or charged it could pull one CELL lower that the rest or the limit, which then triggers a protection mode with FETS OFF. Just don't know without the code.
 
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