Lithium ion batteries can be very hazardous. I accidentally started a wildfire this year due to one. It was in my rear tractor toolbox but bounced out while I was brush hogging. The blade hit the battery and ... pow ... instant wildfire. More than an hour later, with the fire out and firemen and equipment everywhere, the battery was still too hot to touch without burning skin. It's a chemical reaction thing.
One thing I might suggest is putting your battery chargers on timed outlets. So you can never accidentally leave it charging for long periods of time.