I've had this issue with every build for one of my email accounts. Not all, but a particular non-google/yahoo/microsoft POP email account would attempt to sync nonstop and burn up my battery. At first turning sync off fixed the issue but I went back to fiddle with it again and once the issue restarted, even setting it back to no background sync wouldn't stop the account from syncing constantly. Once I deleted the account entirely from my phone my battery life has been great.