I’ve been curious about what’s been causing my Nexus 5’s battery to bulge. I’m pretty sure the immediate cause is because of overheating around the battery. Overheating from the CPU (due to running video conferencing for too long) caused my laptop’s battery to bulge and I think there’s some sort of chemical reaction in LION batteries around prolonged excessive heat. But what could have caused the overheating?
I do play some games on my cellphone, but I don’t think enough or for long enough periods to cause the overheating (certainly my battery would at least run out if I was playing for that long). The other hypothesis I have is that my phone could be running hot from trying to acquire location, but again that would have caused my battery to run out a lot faster than it would normally do under normal behaviour (and I would have noticed). My last theory is that using my QI chargers caused the problem. I think I recall my phone being hot while being wirelessly charged, and perhaps the prolonged exposure (charging overnight) caused the battery issue.
In any case, this is one time where I don’t like/agree with Google’s design principle of having non-removable batteries (I also would prefer microSD cards instead of cloud storage).