This article describes a battery charger, which is powered by thermoelectric (TE) power modules. This system uses TE devices that directly convert heat energy to electricity to charge a battery. The characteristics of the TE module were tested at different temperatures. A SEPIC dc–dc converter was applied and controlled by a microcontroller with the maximum power point tracking (MPPT) feature. The proposed system has a maximum charging power of 7.99W: that is better than direct charging by approximately 15%. The objectives are to study the principle of TE power generation and to design and develop a TE battery charger that uses waste heat or another heat source as the direct input power.