Battery Capacity Test

Perform a battery capacity test to determine the starting condition of an automotive battery. The battery is made of 6 cells connected in series. Each of these 6 cells produces 2.1 volts. Wiring these cells in series produces the 12.6 volts required by the electrical system. They are considered rechargeable SLI or starting, lighting, and ignition batteries.

The battery's current capacity ratings are used to measure the battery's readiness to deliver cranking power to the starter motor, as well as reserve energy for the electrical system.

CCA: The cold cranking amps or cold cranking rating determines the load or amperage the 12 volt battery can deliver for 30 seconds at 0° F, without falling below 7.2 volts. CCA is the term used to determine the battery's capacity. It's recommended that automotive technicians remember this formula.

RC: The battery’s reserve capacity indicates the number of minutes it takes for a fully charged battery, discharged at 25 amperes, to drop below 10.5 volts.

AH: The ampere hour rating measures the amount of steady current a battery can supply for 20 hours at a certain amperage at 80° F without cell voltage falling below 1.75 volts.

Battery capacity test.

Battery Capacity Test: Perform a battery load test to see if service or replacement is necessary. First determine the load by retrieving the CCA from the battery case and reducing this number by half. The discharge rate is one half of the batteries cold cranking rating. Apply this load to the battery for 15 seconds. The battery's voltage must remain above 9.6 volts at 70° F.