There's no dressing it up: the 3DS's battery life of 3 - 5 hours is disappointing. Ryuji Umezu, the system designer, talked to Nintendo President Satoru Iwata about the many features that sap away the machine's battery life, with the main culprit, as you would expect, the 3D top screen.
Explaining that the most energy-hungry aspect of most portable consoles is the backlit screen, Umezu goes on to say that while the 3DS has two of these, like its predecessor, the top screen has double the energy consumption of a 2D screen as it has to send separate images to each eye. Separate images means the amount of light delivered to each eye is half what it would normally be, necessitating an increase in brightness to maintain the same level of screen illumination.
The console will implement an active backlight system to alter the screen's brightness according to what content is being played on it, in a similar way to some HDTV's dynamic contrast functions. When the screen is mostly dark, the backlight is turned down as it's not needed as much, but this power-saving option is completely optional.
Umezu claims that playing games with the power save function off and brightness turned to maximum will give around three hours of battery life, but turning the active backlight on can squeeze another 10-20% out of the battery, giving around an extra 20 to 40 minutes playtime. Setting the backlight to its lowest level will give you around five hours of play, but naturally the active backlight has less impact here.
Nintendo recommends gamers use their charging cradles every day to recharge the 3DS's battery, as even with the power-saving options turned on it sounds like players will be doing a lot more charging than usual.