How to Check Your Vehicles Battery

Basic Automotive Battery Terminology

An automotive battery is a rechargeable SLI or starting, lighting, and ignition battery. It is a 12 volt battery made of 6 cells connected in series. Each of the 6 cells produces 2.1 volts and wiring these cells in series produces the 12.6 volts required by the automotive electrical system.
The batteries current capacity ratings are used to measure the batteries readiness to deliver cranking power to the starter motor as well as reserve energy for the electrical system.


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.


The batteries reserve capacity indicates the number of minutes that a fully charged battery can be discharged at 25 amperes before it drops below 10.5 volts.


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

Battery Capacity Tests:

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 batteries voltage must remain above 9.6 volts at 70 F. Remember that battery voltage is relative to temperature, and to compensate remember the lower the temperature the lower the voltage.

A specific gravity test determines the weight of a certain volume of liquid divided by an equal amount of water. A fully charged automotive battery has a specific gravity of 1.265. As the battery discharges the specific gravity becomes lighter and more like water, closer to 1.000. The specific gravity of a battery is a good indication or its state of charge. Use a hydrometer and adjust to temperature by adding .004 for every ten degrees above 80F and subtracting .004 for every10 degrees below 80F.

Now, If your reading this and still feel you need help diagnosing your battery or just don’t have the proper equipment to test these thing on you vehicles battery, fell free to Contact Us for an appointment. MDH Motors offers free basic electrical system checks to new and returning customers.

This post was written by: Martin Hand


If you find this information helpful please consider a donation. These articles, questions and comments are very time consuming so even a small donation gives me motivation to keep educating automotive owners. Donations will allow us to continue open questioning/comments, automotive education and repair tutorials in the future as the business grows. All proceeds go to the expansion and maintenance Thank You

MDH Motors logo

About Martin Hand

ASE Certified L1 Advanced Mastertech. Martin Hand has over 15 years experience in Asian and European Import Auto Repair. Specializing in electrical diagnosis, engine performance, AT/MT transmission repair/rebuild. Martin is also pursuing a degree in Computers Science & Information Systems starting at Portland Community College while he plans to transfer to OIT. Certified in Java application level programming, experienced with other languages such as PHP, Ruby, JavaScript and Swift. Martin has future plans of automotive diagnostic software development.

Leave a Reply

Your email address will not be published.