Abstract: A battery adapter assembly for engine-powered outdoor power equipment including a battery pack, an adapter, a receiver, and a starting motor. The battery pack includes multiple battery cells, a positive terminal, and a negative terminal and is removable and replaceable. The adapter is structured to selectively connect to the battery pack and electrically connect to the positive terminal and the negative terminal of the battery pack. The receiver is structured to selectively receive and electrically connect to the adapter to transfer power from the battery pack to the receiver. The starting motor is structured to start an internal combustion engine and selectively receives power supplied by the battery pack. The adapter is structured to connect to and transfer power from multiple battery packs having different voltages.