A reserve power source for charging a device, such as a depleted power source or a vehicle. The reserve power source including: a reserve battery which requires activation to produce power, such as a thermal battery or a liquid reserve battery; an activator for activating the reserve power upon one of an electrical or mechanical activation; and a pair of terminals operatively connected to the reserve battery for outputting the produced power. The reserve power source can also include a cable connected to each of the pair of terminals for connecting outputting the produced power to the depleted power source and/or conditioning circuitry for conditioning the produced power prior to output at the terminals. The reserve battery can also include a stop for preventing the activator from activating the reserve power source, where the stop is selectively removable when activation is desired.