Before I came to this forum, I always thought lithium ion battery were fairly safe. I remember sticking any old rechargeable AA battery into my old charger my dad had from his old company (that charger is probably 10+ years now). We leave them unattended for hours and pop them out once its done. My friends also does the same thing, especially those that use power tools and had bigger lithium ion rechargeable batteries. They would occasionally leave their 12-18.5v lithium ion battery for their drills charging unattended while they do something else. Are 18650 battery so prune to dangerous situation that ones must be cautious of overcharge and over discharge? What about those cell phones and laptop people leave charging overnight. I believe that kill the battery life when overcharging occur, but I believe the electronics are built in with very capable technology to prevent accidents.