That looks like a battery protection PCB, yeah. It usually does three things:
- over voltage protection
- undervoltage protection
- overcurrent protection
- reverse polarity protection
Bypassing it would be a bad idea, but it’s also pretty rare they fail. Maybe it’s just in undervoltage protection mode. Try to hook up your variable power supply with 4.2V and a 50-100mA current limit to the battery tabs (check polarity!) and see if the cell takes current. Above 3.6V the battery protection should lift and you should see voltage on the battery output terminals.



















Keep a sand bucket nearby, just in case :)