In Malaysia they break it down into tariff so the more you use, your bill will spike exponentially. The rate are RM0.218/kwh for the first 200kwh, then RM0.334/kwh for 201-300kwh, then RM0.516/kwh for 301-600kwh, then RM0.546/kwh for 601-900kwh, then RM0.571/kwh for 901kwh onward.
Yes, lithium ion battery, if damaged or installed incorrectly, might explode while in use.