It's also important to know how much your 12V battery is drained before charging. Invest in a multimeter to monitor your battery voltage. A fully charged battery should read around 12.6-12.8 volts.

With a smart 12V trickle charger and maintainer, you can revive your car battery in a relatively short amount of time. And this one from GPED is discounted to $22 on clearance at Walmart , 56% off ...