Sealed car batteries are generally sealed lead acid batteries, also known as gel-cell batteries. The gel-cell battery was considered one of the most powerful rechargeable batteries on the market as of 2007. They tend to be quite heavy primarily due to the lead inside. Sealed car batteries should always be stored in a charged condition and never fully discharged. Chemical reactions can occur when fully discharged or charged at too high of a voltage, ruining the battery.
Don your safety goggles and gloves. Heavy rubber gloves are recommended due to risk of electric shock, but leather gloves will suffice.
Open the bonnet of your vehicle if the battery is still attached. Most bonnets open by releasing a latch that's about 18 to 24 inches from the steering wheel, below and to the left, then,outside the vehicle, releasing a latch just under the front of the hood. If your battery is not in a vehicle, set it on the ground and skip to Step 5.
Loosen the bolts holding the sealed battery cables in place, using your crescent wrench. Slide the battery cable connectors off the posts of the battery. Remove the negative battery cable first; it's usually a black cable connected to the negative battery post, which you'll find labelled with a minus sign (-). Then remove the positive battery cable. It's usually red (though some replacement positive cables are black, so be sure) and connects to the battery post that's labelled with a plus sign (+).
Remove any devices securing the battery in place and remove the sealed battery from the vehicle. Securing devices may include straps or brackets and will differ depending on your vehicle. Refer to your vehicle's owner's manual or equivalent if unsure how to remove them. Set the battery on the ground.
Plug the three-stage charger into a 110-volt socket. Connect the charging leads to the battery as follows: positive to positive and negative to negative. Positive leads are usually red and negative are usually black.
Set the charger to the proper voltage. Usually this will be 2.3 to 2.35 volts per cell for the fastest safe charging. The total voltage will differ depending on the number of cells your battery has; this information should be on the battery.
Turn on the charger and allow it to charge the battery for at least five hours.
Turn off the charger and disconnect if from the battery. Unplug the charger and put it away.
Place the sealed battery in the vehicle you removed it from or the vehicle that you were charging it for. Replace any securing devices that keep the battery from moving, in the reverse manner you removed them. If you are placing this battery in a vehicle you did not remove it from, refer to the vehicle's owner's manual or equivalent for details.
Attach the battery cable connectors to the posts on the battery. The order is positive first and negative last. Tighten the bolts on the connectors securely, but not so tight that they will be difficult to remove.
Setting your three-stage charger as low as 2.15 volts per cell will still charge your sealed battery and can extend the overall life of your battery, but it will take longer to charge. 2.15 volts per cell is the minimum voltage for charging a sealed battery. Charging your battery longer than five hours with a three-stage charger will not damage it.
Never charge a sealed battery while it is attached to a vehicle. Damage to the battery or personal injury can occur.