A battery is provided having heat transfer bars that directly transfer heat between the interior layers of a battery cell and the case that encloses the battery cell. The battery does not transfer significant heat from its interior layers to the posts of the battery that reside outside of the battery case. A temperature-controlled power system also is provided that uses multiple, active thermoelectric devices paired with multiple batteries to provide individual temperature control of the individual batteries forming the power system. The multiple, active thermoelectric devices preferably transfer heat to a single radiator on each side of the power system. A method of transferring heat from a battery interior using conductive, active, and convective heat transfer is also described.