I've never had any problems with batteries (I've always had flagship devices) so 2300 mAh is plenty. It's just another number like a gas tank capacity, you don't know how long it'll last unless you know what powers the device and what kinda power saving features it has (like VVT and cylinder shut-off systems in cars).
Galaxy Camera was a good example as it had loads of extra saver features (that SGS3 doesn't have) like when you turn off your screen, data connections are severed and a "deeper" power off function etc.
But then again, I've never had any storage issues either (no offline content excl. apps) as I stream everything since I have unlimited data.