Not sure on this 100%. There is a design that the ARC S goes into protection mode at 25% to preseve itself. I thought it cut off and entered this protection at 15%. It is soley to keep the phone running smoothly. There was a link for this but I can't find it now.
There were also some battery problems witha dodgy batch but these were inthe very first Arc S to be released and were fixed for the next batch.
also with update 2.3.3 Battery life improved. But you must charge the phone to 100% never any less or it will drain away quicker.
This is recommended to save battery life.
1 Turn off GPS, except when needed, makes a huge difference.
2. Turn off Wifi, except when needed, makes a huge difference.
3. Leave 3G on (or off), it makes little difference to battery life. If you have a good data plan, always use 3G instead of Wifi, except when calling via Skype or watching videos (ie, when the connection speed is important).
4. Turn off notifications for all apps, except when needed.
5. Turn off push (e.g. email) for all apps, except when needed.
6. Manually sync calendar, email, contacts, etc.
7. Configure Skype to logoff automatically after a short period, e.g. 15 mins. Skype is the number one battery killing app.
8. Do not use a Task Killer. Uninstall it if you installed one. As noted above, they are a net drain on the battery.
9 Turn off Bacground data - Settings > Accounts & Sync > Background Data this allows app's to transfer data - this could be happening too often and using your power.
