Hi,
There are a few thing to consider. First, push mail which is somewhat expensive - it is the way get instant messaging so every time you have a new mail the device becomes active.
Second, the larger "messages to sync" setting - the more work the app has to do, every time. So if you do have Push enabled, you can consider:
- Reducing "messages to sync" back from whatever at the moment to 50, you can always increase it later
- You can also disable the Push mail or simply enable it on the account/accounts where you need it to reduce battery usage
Another thing you can do is stop Push mail for some/all accounts and alter your scheduled sync frequency. So let say you have two mail accounts in total:
- Exchange account - important you need to get messages there instantly - enable push mail(press and hold on the account -> Options and folders -> Account options -> enable it from there)
- Gmail/Some other mail - not an important email and you do not need to know what's in there instantly - do not enable Push, but set the app to check it say... every hour by long pressing on it -> Special settings -> Mail, receiving -> enable Special settings -> change the "Mail check interval". The back to the home screen log press on the account again -> Options and folders -> Account options -> check if "Scheduled sync" is enabled -> edit the "messages to sync" to say 50.
After doing that you can gradually change your "messages to sync" setting for the 2nd account from 50 to 100, then to 250 and while you do that keep checking the battery usage.