How to Charge a Sealed Acid Battery
- 1). Remove the battery from the vehicle to charge it. Charging a fully discharged lead acid battery off of a car alternator can result in an overcharge and may damage the battery. Use a crescent wrench to loosen the battery cables. Always wear safety goggles and protective gloves when working with lead acid batteries, even the sealed type. The sulfuric acid in the battery is extremely corrosive.
- 2). Use a three-stage battery charger. This type of charger is designed for lead acid batteries and usually costs about $40-60 (as of 2009). Plug the charger into regular house current but leave it turned off. A sealed lead acid battery is equipped with a small tube called a vent tube to permit gases inside the battery to escape. Make sure it is free of obstructions. Connect the positive lead to the positive battery terminal and negative to negative.
- 3). Set the charging voltage. A voltage of 2.40-2.45 volts per cell will give you maximum charging speed. A slightly lower voltage (2.30-2.35 volts per cell) will take somewhat longer, but will help to make the battery last longer. Once the voltage is set, turn the charger on. Allow about 5 hours for the initial charging stage, which will bring the battery to about 70 percent charge. The charger will automatically switch to a lower voltage topping stage, which may take up to 10 hours (the time may be longer for high power storage batteries). Once the battery is fully charged, the charger will go to the low voltage "float" phase (also called trickle charging).
- 4). Reinstall the battery or place it on a trickle charger for long-term storage. To reinstall the battery, turn off the battery charger, and then disconnect the power leads. Return the battery to the vehicle and reconnect the power cables, making sure positive goes to positive and negative to negative. If you don't plan to use the battery for several weeks (if it's in a recreational vehicle you are storing for the winter, for example) leave it on trickle charge or recharge it every couple of weeks to prevent natural discharge from draining the battery.