A dual voltage power supply having at least one battery with multiple battery modules and a first set of switches for connecting the battery modules in series to thereby provide a first voltage to a first circuit in case the first switches are closed and to disconnect the series connection case the first switches are open. At least one connection tap is connected to one of the battery modules to provide its voltage to a second circuit operating at a lower voltage than the first circuit and being connected in parallel by a second set of switches to other battery modules. The other battery modules are connected in parallel to each other and one of the battery modules, in case the second set of switches is closed and are not connected in parallel in case the second set of switches is open, can be charged with off the shelf generators.