Abstract: Apparatus for charging and desulfating lead-acid batteries provides a DC electrical charging current to the battery terminals to charge the battery to a fully charged voltage during a bulk charge mode. When the battery reaches a fully charged voltage, the apparatus switches to a float charge mode where the battery voltage decreases to a float voltage less than the fully charged voltage and is maintained at this level. When the apparatus is in the float charge mode, the battery charging current is turned rapidly on and off to maintain the battery at the float voltage and to desulfate the battery. When the battery voltage drops to a predetermined value below the float voltage, the bulk charge mode is reentered.