Yesterday my FP3 drained completely. In the evening I had about 40%, in the morning it was dead and I had to do the entire procedure with opening the case and pulling the accu and all that.
I had no special or new installed apps running, everything was as every day. Networks were off (flight mode). Normally this takes about 3…5% per night.
Question is: how to make clear what happened? The accu usage pages in the Settings are not very helpful, even if everything is OK. When the device dies these pages are indeed unusable because they only display what happened since the last full charging. The real culprit of a complete battery drain is never to recognize afterwards.
A good idea would be to write an emergency log when the remaining power capacity reaches 5% or so. And the log should then be visible somewhere in the settings.