I would never charge a LIPO on board, however I do charge NIMH batteries on board. I have never heard of a NIMH causing harm until now. The discharge rate is much lower and there has to be an issue with the battery or the wiring leading up to the battery for this to happen. I'll have to re-run that through the risk matrix and see where it ends up.
I would certainly never debate this topic on the FOR charging batteries on board and as Gary said, "it is better to be safe then sorry" My latest builds are made with the thought of removing the battery for charging. Mainly because I discovered Lipos.
Food for thought
Statistically you have a greater chance of a material loss or your life driving your car, and most of us summon up the stupidity to do that everyday.
