His original battery is three years old. I've never heard of one of the major PC manufacturers selling a laptop with a new battery lasted only two hours (aside from some gaming laptops). No battery holds its original charge after three years, you're lucky if it holds more than an hour charge after three years.
Almost all normal laptop reviews I've seen, and plenty of them have been Acers, the laptops come with a battery that provides anywhere from four to six hours of charge when new. If you buy a new battery from Acer I'm sure it will get you back up to the four hour level, or whatever it was when your laptop was new.
I would echo computernewb's advice to stay away from cheap batteries. Buy an Acer replacement, either from Acer or a reputable store selling Acer brand batteries, like Amazon.