How to Charge a Sealed Car Battery
Today's car battery is called a sealed car battery or maintenance free battery. However, calling them sealed or maintenance free is a misnomer. You really won't be able to find a sealed car battery that is maintenance free. The only truly maintenance free sealed car battery on the market today is made for the specialty show and heavy duty market, and usually costs more than $200. In prior days, car batteries had individual vent caps that screwed over the individual cells. Today's batteries have gone away from the single cell caps and are now using cell caps that cover three cells each. Charging a sealed car battery is an easy process.
Step 1. Clean Terminals
Built up corrosion will degrade current transfer during both charge and discharge cycles. Clean them with a solution of baking soda and water and rinse thoroughly when finished.
Step 2. Connect Charger
The connections from charger to battery are red to red and black to black. Make sure the charger is unplugged and turned off before connecting the leads. Some professional mechanics will say that you should carefully pry the cell vent caps off to allow boiling hydrogen gas generated during the charge cycle to escape and vent.
Step 3. Set Charge Rate
For a battery that is deeply discharged, you're going to want a slightly lower charge rate in order to ensure a complete charge. Fifty Amps is the highest charge rate you should use unless you're boosting the battery to start your car.
Step 4. Observe During Charge Cycle
Typically, if your battery is dead flat, or completely drained, it will take around four hours to fully recharge it. You should check on it and observe its condition and temperature during charging. If the sides appear to be bowed out or the case feels extra warm, discontinue the charge and allow the battery to cool.
You will know when your battery is fully charged by observing the charge rate meter on the charger. It will read zero or very close to it. One important item of note is that you should always charge a battery in well ventilated areas and preferably outside.