In addition to trying out the Zoom for the Kinect, the Nyko company was also kind enough to supply yours truly with the Power Grip for the 3DS. All mobile devices have a need for power, which is why companies keep making external batteries for them.
After all, everybody has a story about how the battery on their mobile device died at an important time. The Power Grip is for those who love the Nintendo 3DS, and it is designed to extend the battery by 300 percent.
One of the biggest problems with external batteries is that they tend to create too much volume on the mobile device itself. In the case of the Power Grip, it adds some ergonomics. I don’t know if your 3DS case will fit with it.
Another advantage is that it clips easily to the back of the 3DS, with no need to remove the internal battery or the back cover. All that is required is to recharge through the standard 3DS AC Adapter.
Perhaps you are looking for one of these cases for the 3DS for like a long road trip, cross country flight, or just want to play extended games at home. Whatever the reason, you should be able to get the Nyko Power Grip on the Nyko web site for a price of $29.99.