Battery Load Testing

2000 S10 Blazer, the Advance Auto battery is a little over 4 years old. The two previous batteries (AC-Delco 75-60) lasted 3.5 years each).

The battery is charged on a regular basis with a Battery Tender charger. It was on the charger for 12 hours last weekend. The battery voltage is 12.7 volts. I put a load on it by turning on the headlights and interior lights. The voltage dropped to 11.9 volts. After shutting off the lights, the voltage was 12.4 volts. Is there anything else I can try to get an idea of the battery’s condition.

Would an inexpensive Harbor Freight battery load tester give a better indication of the battery condition or am I better off taking it to Advance Auto to have it tested?


Ed B.

Ed, Is The Truck “On The Road” ? The Guys/Gals At Advance Will Test The Battery/Charging System For Free. That’s What I’d Do.


I get my battery tested for free at the Advance Auto Parts store. You should do the same.

Don’t know if the HF tester is good or not. It is likely better than doing nothing at all to load test your battery. I have had good luck with other HF tools.

I have an informal battery test as follows: Turn the headlights on bright, start the engine and immediately stop it. Then repeat the start and stop routine about 10 times. If the battery continues to start your engine then the battery has some life left.

Before electronic ignition as it is now was used, I used to ground the ignition coil wire and then run the starter motor for about a half minute. That also would indicate some battery life remaining. Running the starter much longer could overheat your starter motor.

With a single fuel injector, it was possible to disconnect the injector to run the starter for a half minute without an engine start.

I suppose there is a simple, safe way now to prevent an engine start in order to test a battery as mentioned but I have not done that. It should work to pull the fuel pump relay to prevent continued fuel delivery.

I called Advance and they said the battery could be tested in the car. The battery had 280 CCA out of a rated capacity of 650. I decided to replace it for the winter.

Thanks again,

Ed B.

Good thinking. You probably saved yourself facing a half day of grief beginning one cold wet morning.