The 3DS has a battery that lasts at MOST 3 hours? This rumor says a maximum of 3 hours. So we could be looking at less than 2 hours depending on brightness and other settings, or the intensity of the game.
we don't really know how they are running the system, this info comes from ubisoft devs who leaked info, there is still no direct confrimation, don't swallow word from word about it.
that said, the original 3DS lasted about 3:30 hours on the 5th brightness, about the same as this, it is similar, min-max setting are still unclear about the NS, but we should be waiting for that.
and even in that case, I'm not that concerned, I usually end up playing in a place where I can charge it at hand.
we must remember we are very delayed in battery energy developments, cellphones last about a day in this era, Nintendo isn't out of this cycle to magically put a 15 hour pack inside a system targeted to a mass market