I will agree with the above. My industry literally runs on batteries, and the dangers associated with them are real. Ok, ours are mainly Lithium based batteries, and they can be very nasty, but the problem more lies with the electronics in whatever charger you are asking to charge them. I have a growing list of clients that have lost houses, cars, boats, and more recently the life of a young drone operator to a battery fire.
Please don't get complacent peeps. Batteries can be nasty little things when it all goes wrong.
I know it's after the fact, but I would never charge a battery while still mounted in the plane, car, boat, bike or anything else for that matter. Charge in a clear well vented area.
PS - My motorcycle was supplied with a battery tender setup, and I won't even use that. If I need to charge the battery, I yank it from the bike.