Location services can prompt large drains on any smartphone's battery: they use a combination of the Wi-Fi network name, where available, plus mobile mast data and GPS sensor input, to calculate the phone's position. The mobile mast data, for example, is usually calculated by comparing the strength of signals from the three nearest phone masts and triangulating against them. However if such a calculation is made too often, by polling the masts, it will begin to use battery power unnecessarily.
I'm on 5.1 as of a few days ago.
My 3gs goes from 100% charge over night, to 73% in two hours only on stand by.
not one single text or phone call in or out.
All apps are off, icloud off, bluetooth off, mail off, push off, location sevices off, wifi off.
******* everything off!
If this not solved in the next week or two, I'm chucking this phone and moving over to an android phone.