The 18 amp panel mountable battery charger is complete with a button-activated battery and alternator tester for 12V lead-acid batteries and features a 3-step charging process. 3-Step Charging Process:Constant-Current Charge -- when the battery voltage is lower than set point, it will charge the battery at the max. current which is called quick charging. Constant-Voltage Charge -- when the battery is almost been fully charged, the charger will limit the current automatically. Float Charge -- when the battery voltage reaches the settled float voltage of 13.5V, it will automatically switch to the float charging condition with the current of 0.1A~0.3A.