Nikon updates firmware for D3100, D3200, D5100, D5200, and P7700: Digital Photography Review
I guess the new firmware must identify EN-EL14 vs. EN-EL14a and the check fails with a 3rd-party battery. Probably a bug in the new firmware as Nikon may simply have skipped a test for 3rd-party batteries in the lab. Solution would be to fall back to EN-E...