Two suggestions:

1. Modest might have an impact on battery drain. I switched to Claws, much more powerful, and deleted my email account on Modest. (AFAIK it is not possible to un-install Modest using App Manager.)

2. Are you using an SD-Card with your device?

I have an N800 and tried two Kingston 8 GB Class 6 cards for a while. They would also drain the battery overnight with no WiFi on.

Since I switched to two Sandisk 4 GB Class 4 the battery lasts for at least a week with no WiFi.

Maybe just take the SD card out for a few days and see if it helps.