NiMh are stable, but they get very hot when charging. I had a NiMH battery catch fire once - its not pretty. Chemical fire that is hard to extinguish. I accidently overcharged it (quick charged it too fast). It was a brand new $40 battery. I was lucky to get it out of the house before it damaged anything else (other than the battery). If it was in a model it would have burned it up and got leaking acid all over. I agree with others - no charging NiMh, Ni-Cd, especially Lipos - inside a model. Bad idea.

The only batteries that can be safely charged in the model are sealed AGM motorcycle or watercraft batteries - those are too big for 1/16 scale. Even then its a good idea to have them out of the model if for some reason they should get hot during charging.
B