Help identifying lithium battery pack

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I pickup up a surplus battery pack really cheap, but of course it came with no documentation. The pack was new, still in the bubble wrap, so at worst I can take it apart and use the cells separately, but I'd prefer to use it as it was designed.
The pack contains two 3.7V 820mAh cells in series connected to a small circuit board. On the board are two ICs. The larger IC is an 8 pin SOIC with the markings WB on one line, and 6M4 on the second. All four of the pins on one side are connected together but the PCB trace, so I suspect this may be a mosfet or power switch of some sort. The smaller IC is a six pin SMD package with the marking PAKG.
I've tried using Google to look up the markings on the ICs, but can't find anything useful.

Can anyone help identify any of this, or at least point me to where I can find more information?

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That's PCM - protection Circuit Module. These are used for limiting discharge current and level.
The battery packs shall be lithium based chemistry, methinks.
Since the pack is already fitted with this, there's no much sense hacking: batteries with this chemistry are dangerous. On the other hand, PCM's are designed to be transparent for the application.
CPF should contain a plethora of reading.

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One chip is probably a coulomb meter (does the pack have an LED bargraph display showing state of charge?) or a one-wire interface to whatever it originally plugged in to. The protocol may be encrypted to prevent use of an unapproved charger. The other is almost certainly a permanent disconnect that triggers if cells ever drop below a safe voltage. Overdischarge dissolves copper from the anode which would replate on the next charge, possibly shorting the battery. Those bags look like lithium polymer cells, with a maximum voltage somewhere around 4.2 volts. If you bypass the protection, do the first few charges outside on a concrete slab or in a barbeque grill.

Properly designed (i.e. within the last few years) lithium iron phosphate (LiFePO4) cells do not have an excess of lithium, copper does not dissolve on overdischarge and the replating/shorting risk goes away. But those would want charging to 3.65 volts maximum.

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M1 is most likely a dual FET that is being switched by U1. I highly doubt coulomb counting is happening on this PCB. None of the resistors are of the proper value and there do not appear to be any data connections or anything of that sort.

U1 is some sort of undervoltage/overvoltage protection of some sort. I don't recognize it though.

What are you trying to accomplish? If the PCB is working properly you should just be able to attach your load to the pack, and it should cut off when the pack has discharged as much as is safe for the cells.

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Agree - the little board is a protection module. Those things can catch fire if the discharge current is too high. And, they can be damaged if discharged too deeply or charged too much.

Yes, you should be able to charge and discharge through a single set of pins on the board.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net