According to this link, it is possible to also remove the
D3100 battery check, but as yet that's about all you can do with the D3100 firmware patches. The D5100 has more patches available to it. But there are already 'unlocked' batteries that work
Nikon-Patch
And, if you look hard enough can also find decoded batteries that don't need this firmware hack (and are also a larger capacity) so you can also now have a spare instead of having to buy a battery grip (if you don't have one yet). But a dying battery and having to change it in the middle of a shoot wouldn't be very helpful though
Try searching
Amazon UK for DSTE EN-EL14 1350mAh
I bought something similar a couple of months ago but the seller wasn't allowed to ship outside China (apparently the China post office refused to ship to some countries and UK was one of them so I got a refund). Shame really as I wanted to see how good they really were before I bought another one
