I have never had a problem with the 110v Foxpro charger but I could see how universal chargers could cause a problem. Foxpro absolutely recommends the battery door be open when charging and states to not charge the batteries more than 10 hrs with the Foxpro 110v charger. Mine makes them nice and warm to the touch but never hot. I have had zero luck with regular alkaline batteries the time or two I have used them. My unit eats them in no time flat. I dont use the vehicle fast charge system with mine since I carry around another set of fully charged rechargeables if the one set gets low. Rarely ever happens but good to have a backup.