Thread: Second battery charging.

It will drain your main battery. It's supposed to draw power from a second battery to keep your main battery charged. If you reverse that, it will drain your main battery to keep your second battery charged.

Pretend you watch a movie on the carputer battery for two hours. It drains the carputer to 10.5 volts. You then leave for some reason without driving the car. The carputer batter will begin drawing power from the main battery until the voltages are equal. Don't know where that might be, but say it's 11 volts. When you go to start the car, it may or may not start.

Not saying it won't work outright, probably will. But just when you get comfortable with it, it may strand you.

Now, if you put a relay on that battery that only opens when the car is ON, that might work. That way it would only recharge if the car was operating.