An auxiliary battery attachment apparatus, which is attachable to a first housing containing a first battery, includes a second housing, a second battery disposed within the second housing, positive and negative couplings, a one-way charging circuit, and at least one switching device. The coupling(s) are respectively coupleable to positive and negative terminal(s) of the first housing. The second housing includes positive and negative terminals, which are electrically coupleable to an electrical system. The charging circuit is electrically connected between the positive coupling(s) and a positive output of the second battery, and facilitates charging of, but prevents current flow from, the second battery when the first battery is supplying electrical energy to the electrical system. The switching device(s) is operable in at least two states to electrically connect the positive terminal(s) of the second housing to a selective one of the positive coupling(s) and the positive output of the second battery.