Bad Car Battery

Recommended Battery jump pack.

Ever wonder how a battery goes bad?  Ever wonder what the easiest way is to check a battery with a voltmeter?  This battery was a 4 year old Napa battery that was under warranty and was replaced at no charge except for the pro rated cost. The customer was driving home from work and stopped to get gas but was not able to start the car back up again. I was able to get the engine started using a battery jump pack and bring it to a safe place to hook up a voltmeter to check the battery.  As you can see below, using my Fluke 87 the battery is obviously bad. It is a 12 volt battery (12.6 volts fully charged) and the alternator was charging when the engine was running so there should be no reason for low battery voltage like you see in the pictures and video below. If there was a draw on the battery with the vehicle off, there would be no way it could drain a battery in the amount of time the customer stopped to get gas. So the only explanation is a bad battery. Notice I did not load test the battery. Just used a voltmeter. Of course a load test is the best test, but using a voltmeter is accurate as well. If possible, you should always run this test with a fully changed battery. However, keep in mind, if the battery is bad, it may not take a charge. You could charge it for hours and hours and it may never get back up to 12.6 volts like it should. This is another indication that the battery is bad.

If you having troubles with your car battery draining while the vehicle is running or while the vehicle sits overnight and would like some assistance in diagnosing this concern, click here to chat with a mechanic.

This happens because the cells inside the battery break up causing this sort of voltage condition.  You can see the two pictures below. The first picture is the battery voltage with no load.  The only load or draw on the battery was the dome light was trying to illuminate because the drivers door was open.  A good strong battery would have no problem with this small amount of load.  The second picture is the battery voltage with the key on.  This puts a load on the battery because this powers up several components on the vehicle and this is where you will see the integrity of the battery.  Not only the battery voltage was much lower with the key on, but the battery voltage was very unstable because the battery is bad.

If your vehicle sits for a long period of time between uses, it is recommend to use a Battery Tender to to keep the battery fully charged when not in use. This will prolong the batteries life and allow you to get the maximum use out of the battery.

Here is a Portable Battery Jump Pack I recommend (with compressor).

If you find that using a voltmeter to diagnose a battery can be a bit difficult and confusing at times, you can always resort to using an Electronic Battery Tester. All you need to do is hook it up to the battery, plug in the cold cranking amps and hit the “test” button and it will come back with a “good” or “bad” reading.

Of course, always be sure that the battery cables are clean and tight and have a good solid connections. Just because the terminals are tight does not mean that it has a good connection. I see this mistake made a lot when talking with this customers. If you have a top post battery connections (compared to a side post battery), then you can use a simple Battery Post Cleaner to clean the connections. Also, don’t forget that water will do a good job cleaning battery acid from the terminals.


Taking a voltage reading from the battery
Fluke voltmeter reading bad battery at 8 volts
Fluke voltmeter reading 4 volts from bad battery
Taking a voltage reading from a bad battery reading 4.11 volts

If you think you have a bad battery, faulty starter or possibly a drain on the battery and would like help diagnosing it, click here to chat with an Expert that specializes on your vehicle.