What's Wearing My Car Battery Down?

courtesy of Bob, The Auto Answer Man


Hi Bob,
Have you every heard of an auto alarm wearing down the battery in a car while in the valet mode? I own a 95 Neon that has a Viper 4000. Twice in the last month my car battery has gone so weak that I couldn't start my car without being jumped and both times the car alarm was in the valet mode. My husband and I think there might be a short somewhere. What do you think? Should we get the alarm disconnected? Or just never use the valet mod? Thanks!
Kellie B.

Kellie,
Any time you have a situation that the battery is draining down and not being able to start the car there are a few things that you can do to try to determine what is happening. First, batteries will normally discharge when not in use. I am assuming that this is a car you use every day. For example, I have a 72 Chevelle that just sits in my garage. It only goes out on the road but maybe twice a year in the summer. About a week before I decide to take it out, I must recharge the battery. I also leave it disconnected from the car when not in use.

This brings me to my next point. If the battery is still connected to a car and the car is not driven long enough then the battery will never recharge. But, the car even if not running will suck energy from the battery. If you have a modern computerized (85 or newer) car, then the on board computer will use energy. If you have a digital radio, then that will use energy. If you have a clock running then that will use energy. Auto alarms are one of the worst culprits!! they are always on! I do not know the details about your Viper system, but I will look into it.

To put things into perspective, let me tell you about a story that I just went through on my Wife's car. She has a Ford Taurus, and was getting a battery light on the dash. I check it out and found that the belt was slipping. Okay cool, there is the problem (I also found that the battery was in poor condition, replaced it). New belt here we come. Fixed that, then was still getting a light (on constantly). OK well then that could only mean that the alternator is weak. I replaced that.

Now the light comes on when cold but goes out. Okay, now what is this. the only thing left in the system is the voltage regulator ( on this particular car, the regulator is separate from the alternator, sometimes it is integral). I replaced the regulator, now the light does not come on at start, but a few minutes later. Hmm... what could be causing this.

Now my wife only uses this car for short trips, back and forth to college and work (the total of the trip per day is about 10 miles round trip). This has been going on for a while, but I was not that concerned because the battery light would go off after about 5 minutes. While I was thinking of other possibilities, my wife had to take a long trip somewhere. After this trip, the light never came on! The reason is that the alternator fully charged the battery during this trip! I could have made my life easier if I just put the battery on slow charge overnight when I first changed the alternator. I guess hind sight is 20/20. One other cause for this could have been a faulty ground connection. So I would ask you to check all the wiring under the hood of the car. Check all connections coming off the battery. And fully charge your battery.

Now after all this, the battery still drains, then either try to fix it yourself (I'll give you some pointers) or take it to a certified repair center. If you want to check it yourself, you will need some tools, like a volt meter and a test light (both of which could be purchased from radio shack). Now with the engine off check the voltage of the battery. It should be somewhere between 11.5 and 12.5. Now start the car. It should read 14-15 volts. If it does then the alternator is working. Now turn on all accessories (lights, fan, AC everything electric) and check the voltage. If it drops below 12, bad alternator or regulator. If not, then the charging system is ok. Now turn off all accessories, turn off the car. Disconnect the negative terminal from the battery. Install your test light between the negative post and the cable you just removed.

If the light shines, then you have a current drain (off, make sure the key is off and the door is closed, and if you have a light in the engine compartment, unscrew it, this will cause a drain). Now if the light is on, go into the car and remove one fuse at a time until you see the light go off. At this point you have found the circuit that is draining the battery. If you have gone through all the fuses and the light is still on, then I would suspect that the place that installed the alarm might have done something wrong. otherwise there is a short between the battery and the fuse panel. All of which are difficult to find. Go through this, and let me know how it turns out.
Good Luck!
Drive Safely!
Bob, The Auto Answer Man


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