The problem is lithium doesn't like being at 100% state of charge for prolonged periods of time. Normally you charge it up, then use the battery. When on a char

The problem is lithium doesn't like being at 100% state of charge for prolonged periods of time. Normally you charge it up, then use the battery. When on a charger the voltage will sit close to fully charged voltage, and that ages the battery quickly. Add some heat and you may have a problem eventually. In my experience, its usually "only" a problem when later, you discharge the battery and then try charging it back up, thats when stuff starts burning.