Just thinking about this further: let's assume for a sec that this battery time is indeed with the 3DS on its most power-saving efficiency settings. Now, factor in the brightest option for the screen to go on, Wi-Fi settings and online play, with maximum volume to boot; if the DSi drainage is any indication, that would shave off nearly 3 hours of play time.
Honestly, that few hours on a Nintendo handheld? Really can't see it people. Add in the bigger battery, and I'm a sceptic of these claims. I'll wait for official confirmation or hands-on experience.