I have the older PSP, but I have both the standard and high-capacity batteries, which last about 3 & 6 hours with normal drain. I play Metal Gear PO online alot with the high-cap battery and that lasts me about 2 an' a half hours between the streaming and loading from disc. Both batteries are the same size and I THINK there's a special battery cover you can buy to use the older batteries with the slim PSP. Also, there's a setting in the main menu to power save the Wi-Fi, but I'm not sure how much extra battery life it gives, since I don't really use it.