I ran some test with powerboost 1000C, and I have some issues with overheating.

I tested different 3.7V lithium batteries and they don't have the same symptoms.
I have 4 different batteries from 2 different suppliers.
- Two with blue wrapping, 5700 mAh and 3900mAh
- Two without wrapping, 5000mAh and 2500mAh
The blue wrapping lipos can be connected to JST PH, but then when micro USB is connected MCP73871 is overheating like crazy, up to burning my fingers. However charges seems to be going on and MCP73871 does not go into overheat mode (only charge LED is ON), even after the whole PCB is burning hot. (without load connected)
The two lipos without wrapping can not even be connected to JST connector. When connected (and micro-USB unconnected, and no load connected) MCP73871 will go even more hot instantaneously. I did not tried to connect micro-USB charger.
This second error sounds like a battery polarity error, but I can assure you that it's not. Polarity is the same on the 4 batteries and triple checked. All batteries have been tested batteries with other charge system (TP4302 power bank IC PCB) and they are working correctly.
I tend to think it might be a problem with the battery protection PCB, as both batteries from same supplier behave the same. There might be some kind of incompatibilities. Any hint?
From your experiences does the powerboost heats a lot?