The CH100 Charge Controller is designed to work with maintenance-free deep-cycle lead-acid batteries. The voltage of the charger is slightly different than what is required to charge the marine-type flooded-cell battery. Therefore, Campbell Scientific recommends purchasing a deep-cycle battery, such as the BP12 or BP24, rather than a flooded-cell battery. Note that our regulated solar panels, such as the SP20R and SP10R, are intended to be used with, and connected directly to, a user-supplied flooded battery.