Automotive Lead Acid Battery Testing and Maintenance
Automotive lead acid batteries are made up of stacked lead and lead oxide plates. The plates are surrounded by an electrolyte solution. The make-up of the solution is 35 percent sulfuric acid and 65 percent water.
A fully charged "12 volt" lead-acid battery is about 12.6 volts.
While charging you need to drive it at about 13.5 to 14 volts to make the current flow in.
Primary tests
- battery voltage test
- charging test
- cranking/amp test
Testing Lead Acid Battery with Hydrometer
Check the cell electolyte density with a hydrometer. The density will change as the battery takes a charge.
Most modern car batteries are sealed, however, many motorcycle, ATV, and other utility batteries allow access to the solution inside. With the battery full charged take readings from each cell. Insert the hydrometer into each of the openings and take measurements. The reading on the hydrometer will tell you the specific gravity of each cell. There should be no more than .05 differences between the cells. The specific gravity should be above 1.225 or the battery is defective or near end of life.
Testing Sealed aka Maintenance Free Lead Acid Automotive Battery
When charged the battery should read on the volt meter greater than 12.6 volts and less than 14.0 volts.
If the voltage appears low it is not necessarily proof of a defective battery. A vehicle with a defective alternator may fail to maintain the battery charge. Also, a battery that has not been in use for an extended period of time, or under very cold winter conditions may also read low voltage.
Determine if the battery is capable of being charged and holding a charge can be done with a rapid charger and volt meter. Perform a rapid charge with a battery charger capable of "rapid" or "boost" charging. Take a voltage reading with the voltmeter. If the voltage rate quickly climbs and exceeds 14.0 volts, reading as high as 17.0 volts, the battery cannot contain the voltage and is defective. Replace the battery.
See also: Lead Acid, AGM, and Gel-Cell Batteries
