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Re: Battery drain overnight...
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Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Wed, 13 Aug 2003 06:34:40 Share Post by Email
In Reply to: Battery drain overnight..., CalAero, Tue, 12 Aug 2003 20:19:48
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I see three possibilities-
One, there is some large current drain in the car. Typically this is a trunk light stuck on. If your power antenna is stuck, that can do it also. However, this is pretty rare, and a new battery should be able to drive a trunk light overnight and still be able to start a car. I'll recommend a troubleshooting technique in a bit.

The second, and what I think is the more probable than a stuck light, is that the battery isn't being charged sufficiently. When you're driving, what is the voltage measurement on the EDU display? The voltage should be in the 13 volt range. If not, then the battery isn't being recharged. The alternator should provide all of the car's electrical needs when the engine is running, and have enough left over to recharge the battery from its starting effort. Putting a totally dead battery on a charger for a few hours may give it enough ooomph to start the car, but if it isn't being recharged by the alternator, then it'll die soon. If you're seeing voltages in the 12 volt range while driving, you may need a new voltage regulator.

Third- this is what I think is most probable - you have a defective battery. Yes, it happens. A battery warrantee states that they will replace the battery if it dies before its rated life; it's not a guarantee that it won't fail. If batteries didn't have defects, there would be no warrantees. It is possible that your battery has an internal short and it's self-draining. Also, car batteries aren't designed to be fully discharged - every time they are fully discharged, they lose a lot of their life. You can charge them just fine, and bang, the next day they're flat again.

The first thing I would do is check the voltage at the battery with the engine running (use a voltmeter) and compare that with the EDU display. Make sure you see the charging system is working properly. If it is, I would then go back to whomever sold you the battery and ask for a new one. For most quality batteries, you should still be under the 100% replacement phase.

Lastly, if you really want to chase current drains, get yourself a good voltmeter with a current reading capability of at least 1 amp, preferably 10 amps. You'll be disconnecting the battery, so be prepared with the radio code, etc.
Step 1 - disconnect the negative cable from the battery. Jumper the negative cable to the negative battery post with a piece of wire. In parallel with that wire, connect up the amp meter, set to the highest range (10 amps, preferably). Wait at least a minute. Check at the fronto fo the engine compartment - there may be a little pushbutton switch on the front cross-beam that gets hit when the hood closes. If you see that button, put something heavy on it to keep it closed.

After a minute, remove the jumper wire. You'll now see the 'quiescent' current drain. A normal drain is about 30 milliamps - that drives the clock, radio, and alarm. A healthy car battery can supply 30 ma for weeks. I wouldn't worry unless you see over 100 ma or more.

OK, why work so hard with jumpers? When you disconnect, then reconnect a car battery, a bunch of electronics reset. They pull lots of current to do this. Normally the dome light will come back on, and needs to time out. If you just connected up your ammeter, it would see a large current draw. Depending on how your meter is fused, you could blow the fuse in the meter. Instead, you let the jumper wire carry that load, and you wait a minute for all the electronics to reset, and for the dome light to go out.

OK, so what if you see an amp of current being pulled? Well, open the fusebox, and roll the window down, then reconnect everything and wait a minute. Now, start unplugging fuses until the high current load goes away. Remember, You Must Reconnect the Jumper before you plug the fuse back in. Why? Because it's just like disconnecting the battery. Why roll the window down? Because if you open the door, you'll trip the dome light. Yes, this method is a pain.

Why disconnect the negative lead instead of the positive? Safety. The entire car chassis is ground. If you bridge across the battery terminals with a wrench, you'll get sparks, heat and a potential exploded battery. Not only can you damage the car, you can get pretty badly burned. If you disconnect the positive lead, when you have the wrench on the positive terminal, not only do you have to avoid the negative terminal, you have to avoid every other piece of metal on the car. However, if you disconnect the negative lead first, then all you have to avoid is the positive post; if you accidently hit the chassis with the wrench, you're just connecting negative to negative, and nothing bad will happen.

posted by 192.249....
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