Considering the NGP was literally just announced 12 hours ago, any rumors that we will hear should be taken with a grain of salt. But it appears that Eurogamer has heard from an unspecified source that the NGP will only be able to last for a maximum of five hours, possibly only four. Now this isn’t something that would be too surprising as the original PSP itself had a short lifespan compared to other handhelds at the time.
Also it is easy to see why the battery life would be so low, considering the fact that the NGP will be running a lot more advanced materials as well as providing stellar looking graphics from what we have seen so far. Of course also keeping a track of where you are while supporting 3G too. So while this is just a rumor at best, it is easy to understand why the battery life is so minimal. Possibly they will sell separate rechargeable batteries to give owners a chance to use it on long trips.