All car batteries are rechargeable, and the best way to recharge the battery at home without the car running is a car battery charger. Car batteries are meant to recharge themselves while you drive, so you should only rarely have to recharge your battery at home. Battery chargers are not very complicated to use, but if used incorrectly they can damage themselves and the battery. To make sure you know what you’re doing when you use a car battery charger, read these step-by-step instructions.
There are two different variations of the 12v battery charger, the trickle charger and the float charger. A float charger can detect when a battery is full and automatically stops charging when the battery voltage is at the appropriate level. When the charger senses a drop in the voltage level, it resumes charging. This type of charger can be left connected to the battery indefinitely. The other type of charger, a trickle charger, has no circuitry to prevent overcharging, and continuously charges the battery whether it is full or not. If you have a trickle charger, you should only leave it connected for as long as it takes to achieve a full charge.
Before using the charger, make sure it is plugged in to an outlet that is grounded. Car batteries are grounded to the frame of the car to reduce the risk of a spark occurring near the battery when connecting to a charger, which could cause an explosion. That way, if you are charging a battery inside a car, you can connect one cable to the frame of the car instead of to one of the battery terminals. Read the battery label to see whether it is grounded on the positive or negative side.
If your battery is grounded on the negative side, as most are, you should first attach the positive cable to the positive battery terminal, then the negative cable to the frame of the car. If it is grounded on the positive side, attach the negative cable to the negative terminal and the positive cable to the frame. Remember to attach the first cable to the battery before attaching the other one to the frame to ensure the spark will be as far away from the battery as possible.
Make the aforementioned connections before you turn the charger on, and be sure to turn it off again before you touch the cables. Some chargers come with adjustable timers, voltage switches or amp switches. Set these to the appropriate level to fully charge your battery before you need to drive again.
Although you may use it only rarely, it is very convenient to have a car battery charger around the hose for when you need it. Since you will not use it very often, it is easy to forget exactly what you should do to operate the charger safely and correctly, so be sure to brush up on the proper procedure before each use.