Unknown circuit board between 2 unprotected 18650 cell pack... Any ideas?

So I bought this excellent little 18650-powered handwarmer a few weeks ago: http://human-creations.com/items/energyflux-4400mah-rechargeable-hand-warmer-external-battery-pack

…but the enclosed batteries are total crap and I want to throw some higher capacity + reliable cells in there which involves a little handy work. I unscrewed the device open and discovered 2x 2200mAh unprotected 18650 li-ion cells wired in parallel with some circuit board between them. It was enclosed within the heat-shrink pack so I’m assuming it’s a PCB…? I e-mailed the company and I’m still waiting for a response to know exactly.

Sorry this isn’t exactly flashlight-related but I thought since some of you geniuses are knowledgeable in the world of li-ion batteries, you might be able to shed some light as to what this board is and whether or not it’s needed if I upgrade the unprotected 18650s with 2 higher capacity PCB protected cells…

Thanks!

Additional info:
The hand warmer charges the parallel 18650s simultaneously via micro USB connection > controller > the pack. The batteries are not to be removed once installed and do not have their own independent voltage checker. The only thing between the batteries and the (+) and (-) leads is this unknown circuit board. The leads solder onto a simple control board which determines low-voltage cut-off, charge status, etc.

The serial number on the unknown board is: XSY-3939 if that helps? :stuck_out_tongue:

This PCB is plain protection circuit, as batteries are in parallel connection you can simply use two protected 18650 batteries connected without existing PCB…

It is similar to the type of protection circuit boards found here.

Thanks very much, guys. And great find on that link LumenHound. :slight_smile: