Hello. Not familiar with your particular charger but, my auto chargers come on at max voltage (20 in your case) when first hooked up and then after a short while ( 20 minutes or less depending on state of discharge) the charger drops to mid range 12 - 10 typically) and then the majority of time is spent on the 'finish' cycle of about 6-8 amps. Not unusual to take 4 to 6 hours or longer. Many variables determine the length of time needed:
1. age and condition of batteries. yes a bad battery can make the charger not turn off as it continues to try to bring a dead one up to charge.
2. type and cond. of charger
3.cable cond. and cleanliness of connections
All modern caps vent to avoid gas build up. You may want to invest in a couple of simple battery testing devices. Like a voltmeter and hydrometer. With these u won't have to guess what your charger and batts are doing or what u are working with battery wise. Good luck !
