Does anyone know if you use more electricity charging at 15 amps for say 4 hours vs. 30 amps for 2 hours? Obviously 30 amps charges quicker but does it use more electricity over a shorter period of time? I can't seemed to find an answer to this on the Internet. I would like to upgrade my house wiring to support higher amperage charging but speed is not really an issue but the cost of electricity is. Any help would be appreciated. Thanks.