Hardware and installation
Lest you get confused, Nyko actually has two distinct products here: the battery itself and the Charge Base which you plug it into. For $19.99 you can get yourself just the Power Pack+ (the battery), but using it sadly will prevent you from using Nintendo's standard charging base, with its trick, flip-out charging contacts. So, Nyko also offers the Charging Base as well, which is $29.99 and includes the battery pack. So, $10 more for the full package, then.
This charging base is rather bulkier than the stock one, and rather blingier too. It features a glowing power light and, when you set the system down, LEDs on the side illuminate your desk to indicate whether it's charging (red) or charged (green). It's a little excessively loud, but is certainly easier than squinting to see the tiny orange LED Nintendo put on the 3DS itself.
Installation of the pack requires the removal of a few screws on the back, pulling off the backplate, and the extrication of the stock 3DS battery. This system completely replaces it. Overall the process takes just a few minutes if you don't lose any of those tiny screws -- or the tiny screwdriver Nyko includes.
Once on the system is roughly one-third thicker than before, though Nyko did thoughtfully contour the back and threw a rubberized coating on there to boot. Naturally this adds some weight, too, up to 280 grams from the stock console's 240. Not a lot, but it's a noticeable difference.
We cycled the battery pack a few times to let things get comfortable before testing, as Nyko indicated that, for the first time at least, you should charge by plugging the stock Nintendo power adapter straight into the 3DS itself. Afterward you can plug that adapter into the base and leave it alone. We would have liked to see a second power adapter included here, and it would have been even nicer if Nyko had moved away from the proprietary plug and gone with a microUSB. Alas, you can't have everything.
We ran a number of tests, each time using Pilotwings as our demo game with the brightness and 3D slider max'd -- how we figure most gamers will be playing it. Consistently we scored four hours of battery life with WiFi enabled. Turned off the system managed just under five hours. The stock 3DS in the same configuration, meanwhile, managed two hours thirty minutes with WiFi enabled, about 2:45 with it disabled.
We should also mention that the first charging base we received would consistently cause the official Nintendo adapter to short out. Put the console in, hit the power button, and the world would go dark -- well, the Charge Base would, anyway. To get it to work again we'd have to unplug the adapter from the wall and let it chill out for a few minutes. Nyko shipped us a replacement, which worked just fine. Hopefully this is an isolated incident, but given our pals at Joystiq had an issue in their first batch too, you might want to make sure you get yours tested long before your return period expires.
So we didn't see quite double the battery life, but we'll call it close enough. That said, the extra bulk is certainly noticeable, and whether or not you can live with it is, of course, up to you -- and the confines of your pockets.