Original Nikon EN-EL14 Rechargeable Li-Ion Battery for D5100 D5200 D3200 D3100 P7000 DSLR Cameras - OEM Compatible with Power Indicator - Perfect for Travel Photography & Professional Shoots - Retail Packaging Included

I was hesitant after reading a few reviews that this battery may not be compatible with Nikon D5100. So far, after 2 cycles, it has been doing great. It has about the same capacity as the Nikon battery. My D5100 has firmware A1.01 and B1.01 (the latest, I think).On any day that I think I may need both batteries, I am going to play it safe by using this Progo battery FIRST, and then the Nikon battery. The reason is that there is always a small chance that the camera may suddenly recognize the Progo battery as non-Nikon and stop (some reviewers mentioned everything was going great for weeks but all of a sudden the camera detected the non-Nikon battery). If Progo was the second battery of the day, you would be stuck with no power for the rest of the day. However, if you started with the Progo battery at the beginning of the day and got the bad news, you could still use the Nikon battery, and just be very fugal in power (not using Live View) knowing that you would have to make do with 1 battery for the whole day. Without Live View, one battery can easily last around 600 shots. With Live View, probably only 200 shots or less. So use Progo before Nikon.