S&S Service Center - Why Not Install My Own Battery?

This morning a new customer had his Jeep towed in because it would not crank over when he turned the key. He had already purchased a new battery & installed it himself, but that didn't change a thing. After a quick diagnosis, we determined that there was a 9 volt drop between the battery positive post and the positive battery cable. This means that of the 12.6 volts in the battery, only 3.6 volts were getting to the electrical components, including the starter. A 12 volt starter will not even grunt on 3.6 volts, therefore the no-start. The battery cables looked clean on first inspection, but it turned out that the inside of the battery cable terminal had enough corrosion on it to keep any current from passing from the battery post to the cable. All we had to do to fix the no-start was properly clean the battery cables.

Bryant & I started thinking about how often we see similar situations & concluded that it warranted a Car Care Tip. Many of the chain auto parts stores offer free battery installation and that's good - IF it fixes the problem. Many times the battery IS dead, but it's because the alternator is not keeping it charged up or there is something staying powered up that is drawing the battery down. That's why every time we get a vehicle with a dead battery, we perform certain tests that MUST be done to verify that the rest of the electrical system is operating the way it should.

We recharge the battery and perform a load test to make sure it will hold a charge and pass enough current to the starter to make it operate.

We then verify that the alternator is producing enough voltage and amperage - one without the other is no good.

We test how much current the starter is using: If the starter is pulling more current than the battery can supply, it might just need a starter.

If the battery will hold a load but keeps becoming discharged, we test for parasitic drain, where something is slowly pulling the battery down. Some examples are trunk and glove box lights that don't go out, and more common now are various modules that stay powered up for a variety of reasons. If we find a draw, it can be maddening finding the cause: We first have to remove fuses and relays one-by-one until the draw goes away, then with an electrical schematic, trace down EVERY item powered by that fuse or relay. Finally, we have to determine if the component is faulty, or if another switch or sensor is commanding it to stay powered up.

As you can see, if you have a dead battery, it quite possibly is more than just a bad battery. It really pays to have it professionally diagnosed.