This week I suddenly had issues with short battery life. After using CPU Monitor Advanced Lite, an app which I can recommend if you want to find which app is using excessive CPU, I found that it was caused by F-Droid. The CPU usage was so few that the battery settings didn’t show F-Droid at all, but it caused frequent wake-ups at such a rate that I couldn’t make the end of the day on one charge which typically works fine even though my battery is slightly old and has occasional hiccups.
I don’t know why F-Droid had started using CPU excessively but after killing the process this morning, it stopped doing so.
Apps that you rarely use can cause a lot of trouble without you noticing! Last year, it was GMail, now it was F-Droid.