my boat has only one battery and it isn't very big, the motor is a 90 hp so it doesn't need a big battery. I have fished all day with 2 electric downriggers going up and down all day without starting the big motor to charge the battery and have had no problem. my kicker has no charging system. the only time I have had a problem is when I sat with the running lights on for several hours without the big motor on. It isn't the best system, two batterys would be smarter but I didn't want the extra weight and it worked for me.