I've been running K-9 Mail since I first got the Droid 1 a year ago. I had it set to check 5 accounts every minute. When I looked at what was taking up the battery K-9 was never very high. However I just changed the settings to 5 minutes for important accounts and 1 hour for unimportant accounts. My battery life has doubled. I think that it uses system resources that don't get reflected in how much battery it uses. Just an FYI.