Oops, haven't been back here in awhile
Hmm, airplane mode & dies in 8 hours. Yup sounds about right. Although if it sits all day in the locker in airplane mode might as well shut it off imo.
That said, root (if not already) and just give a ROM a try. If you like Sense, give Team BAMF's BAMF Forever
specifically I recommend 1.11 version (this has BAMF's Test 3++ kernal already baked in
) which you can get directly in the original post on their own website (no linking here). Once installed, I recommend a couple of extra steps within "BAMF settings":
CPU governor: Try OnDemand vs SmoothAss
I/O Scheduler: Try Noop.
Be sure to battery condition & wipe battery stats(yeah yeah, some folks will debunk. Whateva). On BAMF's site has the most comprehensive method imo. It takes about 2 - 3 full cycles to fully charge then fully empty, but many folks are at least doubling what you currently have.