I've done absolutely everything, restored as new phone, replaced the phone, changed settings. everything. Still can't get more than 5-6 hours of usage and like 10-12 hours of standby.
On my 4S I tried the following a bit of advice on MacTalk I think it was...
Drain the battery so it is off and won't turn on (just before it dies "reset all settings") then charge it back up.
Its put a new lease of life into it.