Lithium ion batteries are relatively safe. The problem is if the batterys substane a hard impact they become unstable and can overheat and start on fire. The Radio Control industry uses them in electric airplanes and helicoptors. They tell you that if you crash the aircraft hard the batterys can become unstable and ignite. Not always but it can happen. Quality of the battery manufacturer can make a big difference. The problems is worse with dell especially when people buy prirated batterys which are not as good as the name brand and are more unstable.