Apologies if everyone knows this already, but it's important and since I've not seen it posted here yet:
Nikon EN-EL15 rechargeable Li-ion battery recall | Nikon Rumors
Although NR says there are no user reports of problems, Thom Hogan thinks otherwise and is urging all to take this one seriously:
Frankly, "service advisory" is too polite a term and too easy for people to ignore. This is a recall by any stretch of the imagination and should be labeled as such in the headline on Nikon's site. And to further label it within the text as a "voluntary" recall additionally softens the language. The bottom line is simple: continuing to use one of the affected batteries is a severe risk and should be avoided.