We make it a habit of not charging any battery-powered tools unless someone is in the shop to monitor the chargers. This just prevents that once-in-a-million chance of a fire.
Battery-powered hand tools have become very commonplace in everyone’s work shop. As these tools have gained more power and torque, the voltages have also increased. Many of these tools now use lithium-ion batteries to generate these higher voltages.. These batteries offer outstanding power for their weight but also require a specific, dedicated charging system. Because the batteries are more highly susceptible to damage during charging we now make a habit to never charge any battery unless someone is present to monitor the charging process.
This is just a safety factor that offers the user the ability to quickly react should one of these batteries catch on fire during charging. While the likelihood of a battery fire during charging is very low, this is just a smart way to ensure there isn’t a problem when there is no one around to quickly disconnect the charger from the wall socket and isolate the damage. You would hate to be the guy watching your shop burn just because you left a battery charger unattended.