Changing a battery
This guide is intended to provide you with a basic understanding of how to service and replace a battery on a common, modern vehicle; not to provide in-depth knowledge of electrical systems. It will assume that you are familiar with the basic principles of a 12V electrical system and components such as alternator, starter, et cetera. Keep in mind that battery acid is corrosive. Always be sure to clean any spills immediately by first neutralizing the acid with baking soda then removing the residue. Always wear eye protection and skin protection when working with battery acid. Lastly, even trace amounts of battery acid will destroy cotton and other fabrics. Even amounts so small you can not feel it on your skin, will put holes in your favorite articles of clothing if it comes into contact with them.
As you know, the primary purpose of an automotive battery is to provide a source of electrical power for starting and for electrical demands that exceed generator output. The battery also acts as a stabilizer to the voltage for the entire electrical system. Most automotive batteries consist of a case, a series of lead plates, and an electrolyte. Most batteries today are maintenance-free meaning that the battery uses little water during normal service because of the alloy material used to construct the plates. Maintenance free batteries are also called low-water-loss batteries. A common misconception of most maintenance free batteries is that they cannot be serviced; They can--in fact--be serviced, but this is not very common. If you believe that your battery needs servicing (maintenance free or not), simply follow the testing and servicing procedures below. Otherwise, quick instructions are also provided on how to replace your battery.
Testing Your Old Battery
Set your multimeter to read voltage and check the terminals of the battery. The open-circuit voltage will indicate the the level of charge the battery has. A reading of 12.6 or higher indicates a fully charged battery, while a reading of 11.9 or lower indicates a discharged battery. Use a 12V battery charger to bring the level of charge up to full.
Servicing a Battery
Battery maintenance includes making certain that the battery case is clean and adding clean, distilled water if necessary. Chemically, water is the only component of the electrolyte that is released while the battery is in use. You should never add additional acid to a battery after its initial fill (which is often done at the auto parts store or battery manufacturer). Taken the time to fill the battery and clean the case and terminals should result in years of trouble free service from your battery.
Replacing a Battery
Replacing a battery is one of the easiest and most common repairs performed. Simply disconnect the battery terminals and battery hold-down clamps and remove the old battery. Install the new battery and reconnect the terminals. It is often wise to use a memmory-saver which plugs into the cigarette lighter socket and provides an alternate source of power to the vehicle while the main battery is disconnected. This will keep the radio and clock set and is especially important on some vehicles with theft prevention systems. Read your owners manual or contact your dealership to determine if this is required with your vehicle.