What risk is that? And how do you know that a similar risk does not
exist with genuine Nikon-branded batteries?
The risk is that if one were using a non-Nikon battery that failed
(short circuited, exploded, some sort of voltage spike, etc), Nikon
would have the right to deny any kind of warranty claim.
Since my camera was bought 2nd hand, this is irrelevant to me, I have no Nikon warranty. And I have not seen any evidence that the risk of voltage spikes, explosions, etc, is any different from a properly working and tested generic 3rd party battery than from a Nikon branded one.
At best, a non-OEM battery is the exact same battery that Nikon
sells, made at the same factory by the same people. That's great.
However infinitesimally small the risk is that a Nikon battery would
suffer a catastrophic failure of some sort, that same risk applies to
the non-Nikon battery. The difference is in possible warranty
implications by Nikon.
Actually, it's perfectly possible to get 3rd party batteries that are slightly better than the name brand ones - for example, Nikon's battery is rated at 1500 mAh, and my aftermarket battery is rated at 1800 mAh. Assuming both batteries actually meet their rated specs, then the aftermarket battery is slightly better. And, as I said, since my camera was bought used, the warranty issue is moot for me.
At worst, a non-OEM battery may look like a Nikon battery and appear
to function as such, but be made with sub-standard production
methods, chemical purity, etc. Many may be perfectly ok, but others
may be woefully inadequate simply due to having too little quality
control or even to the extreme of being made by negligent companies.
It's a gamble. However slight the risk is, it's there.
But if you don't believe me that non-OEM batteries can cause
problems, that's fine. Just ask IBM.
The fact is, major vendors have had the exact same problems with their own branded batteries. Dell, Toshiba, and IBM all had batteries that they re-branded, bought from Sony, that caused these types of fires. These were NOT 3rd party batteries, they were branded by the OEMs themselves, although they did not make them.
In any case, one can tell if a battery is running hot, it's a warning. My clone batteries don't run any hotter than the original Nikon battery does.