Engine-powered forklift comes with a starter battery installed in the engine bay, similar to passenger cars and trucks. The battery is used to energize starter and key electrical components in order to start up the engine. The majority of engine-powered forklift is powered by 12-volt battery.
Numerous types are available, from traditional wet-cell (which requires periodical checkup and water top-up), to maintenance-free AGM or gel-type with varying capacities, depending the size of the forklift truck.
Note that this type of battery is usually designed to provide short-duration, high-powered output in order to crank the engine and is not designed for continuous power draw. For electric vehicle applications, please consider “deep-cycle battery”.