Recently i used K-9 Mail on my Android smartphone (version 4.200). In particular the support for IMAP IDLE and the possibility to use PGP with AGP was very welcome. However, i also noticed that the battery consumption was extremely high from time to time – sometimes the battery was nearly empty after just 10 hours, even with very little usage of the device.
A look into the battery statistics of Android confirmed what i already assumed: K-9 Mail kept the device running all the time and therefore caused the major energy consumption. Now i will try Maildroid. Although Maildroid does not support AGP and the ad-free version is not quite cheap at 14 EUR, it would be worth it for me if the battery consumption would be considerably lower – because a mobile device which will not stay usable even one day does not work for me.