IPhone4 & 4S don't drain battery the same?

My wife and I have an iPhone 4 and a 4s. The 4s sucks power and the 4 simply drinks it slower. The 4s will drain in about 8 hours, the 4 takes about 15 hours. We have tried turning off all Wi-Fi etc but nothing seems to help. Any ideas?

Buy an iphone 5, caus iPhone 4s & iphone 4 are a piece of ****.