Summing up my problems / experiences with the battery performance after using CyanogenMod for a couple of weeks on my fp1: Over time (especially after upgrading to m11) I noticed a steadily growing loss of battery performance over time. The rear part of the device often seems hotter, especially when charging or when extensively using my phone. I can compare with my gf fp1 who uses the original FP OS. Compared with hers, the battery now seems bloated, significantly lasts shorter, shows inaccurate battery percentages (at the beginning dropping from 20 % to 0 in no time. Now even dropping from 40 - 50 % to 0).
I tried to calibrate the battery a couple of times with various apps, but the main problem with that is that I am not able to charge the battery with the phone shut down, as the phone automatically switches on when connected to an active charger. A short search revealed, that it’s probably due to a kernel issue with the costum rom. Trying out other types of chargers didn’t solve the problem.
Another thing I noticed, is that FPOS as well as CyanogenMod display strange MV values (2 - 4 mV while a fully charges battery should display up to 4200 MV - again see attached picture) in the app Battery calibration.
In order to figure out whether the battery is really impaired, I switched batteries with my gfs FP1. Both have been in use for the same time and both were charged with the same charging cables as well as used in similar patterns.
My battery lasted significantly shorter in my gfs FP with FP OS compared with her normal battery. Her battery worked better in mine, still it didn’t lasted as long as her phone.
Another strange thing I found was that sometimes the battery doesn’t only drops dead, it sometimes also gets stucked at 1 % for quite a while (see attached files). With no way to resolve this by calibrating the battery.