Most types of floor machines are offered in battery-powered versions in addition to the traditional electric corded or propane-powered machines. Batteries allow for operator mobility, saving time and contributing to productivity. Scrubbers of all sizes are battery-powered, but different machines specify different battery types. More expensive maintenance-free batteries have longer life cycles, which come in handy for big jobs or when fewer replacements are desired. Gel batteries are also maintenance-free. For a lower cost up front, but a more stringent maintenance schedule, acid batteries are also an option. Battery maintenance is important, however, because no one wants to lose a power source in the middle of a scrubbing job. Operators must have plenty of replacement batteries on hand to ensure jobs are completed.