Do you guys think that they'll improve the battery with subsequent hardware versions?
I'm guessing the battery is pretty slick overall to get that much time. The PSP is basically a PS2, running a monitor and speakers as well. To get 4 hours seems pretty nice to me. The PSP is substantially more powerful then the Gameboys, so it drains a lot more power. I don't mind, since I doubt I'll play on the road anyway for that long. Nintendo has always made the tradeoff for longer battery life at the expense of the rest of the system, not even offering backlights for a while. Just a different philosophy. Nintendo could have went the way Sony has, and might in the future if the PSP takes off.
I bet down the road that developers will get smarter with battery usage, and games will last longer. I wouldn't be surprised to if newer higher capacity batteries are offered, at least third party ones, as technology evolves.