A portable electric heating apparatus for warming a liquid and maintaining the elevated temperature of a liquid held inside a hot beverage container. The housing (23) of the apparatus may be inserted within the perimeter of a bottom rim of the beverage container so that a heating plate (22) releasably contacts a bottom wall of the container. A controller (25) enclosed in the housing includes electrical circuitry for communicating with a supply of electric power and for energizing a heating element (31). In various embodiments, electric power may be provided from wall outlets, USB ports, or batteries, which may be disposable or rechargeable. The heating element is configured to transfer heat to the plate, which warms the liquid through the bottom wall of the container.