Comment by userbinator

It looks like two BL-5Cs, which normally come with their own overcurrent protection (AFAIK even the no-name generic clone cells do), so what's more likely to happen is you trip the protection on one of the cells being swapped. Fortunately these are not very high capacity nor current cells, being ~1000mAh at most. They seem to be pretty robust in general, as a series of hugely popular MP3/MP4 players that used them had nothing more than a diode from USB5V for charging.

On the other hand, I'll gripe about that "schematic" being not actually a schematic but just loose parts with labeled pins.