Battery is going dead

by rogal_tx Mon Aug 31, 2015 7:16 am

Hello, everytime I charge battery ( it's new) it goes dead in 2 weeks of not deriving.
I'm not sure how to identify the issue and where to even start. Any help is appreciated.

by Joe73 Mon Aug 31, 2015 7:59 am

Take a test light. Disconnect your positive battery terminal. Commect one end of the.test light to the batt terminal. Connect tbe other end to tbe cable. So now your test light is in line. Light should be on if tbere is a draw. Start pulling your fuses one by one til the light goes out. The fuse that makes the light go out is the circuit thats drawing power.

by thatfnthing Mon Aug 31, 2015 9:09 am

Best to use a DC amp meter if you can (or volts if amps not available), as it will tell you more than a light. The hook up is the same as Joe described. Also, some things require a constant draw, such as computers or radio memory, and this may be enough to light a test light (depending on the light). However, those things are not sufficient to drain your battery in that amount of time. Those will draw milliamps (1000th of an amp), and you're looking for something drawing somewhere in the whole-amp range.

Also don't forget to test the main feed cable from the alternator, which is not a fused circuit. If you've blown the rectifier bridge in the alternator, the battery will drain back through the alternator when the car is off. The battery will be dead in a couple days.

by rogal_tx Mon Aug 31, 2015 9:20 am

This might be a stupid question but how would I test main feed cable from the alternator?

by thatfnthing Mon Aug 31, 2015 9:35 am

Almost the same way:

1. Disconnect the ground at the battery (this will keep you from blowing the rectifier if it's still intact)
2. Disconnect the main feed from the alternator at the battery, starter, or alternator stud.
3. Hook up the meter -- one lead to the feed wire and one lead to the terminal the wire was connected to (alligator clips help here, since you only have two hands). Which lead doesn't matter -- the meter should read in both directions.
4. Reconnect the battery ground.

If you see amps/volts on the meter, the rectifier is shot. Some units can be repaired (Powermaster is good for this) and some you just have to replace the entire alternator.

Whenever doing any electrical work (especially involving the alternator), you should always disconnect the ground to the battery first, as it's easy to blow the rectifier.

FWIW, another alternative is this: 250 amp relay. Yes it's a couple bucks, but it completely isolates the alternator and you never have to worry about the above hassles.

by rogal_tx Mon Aug 31, 2015 10:41 am

Thanks for the info. Will go through this today.
Will post update.

by rogal_tx Mon Aug 31, 2015 7:46 pm

Ok, alternator appears to be good. When I connect test light on positive side ( in line) the light comes on for a second and goes off than it comes back on for a sec again, ofcourse it continues like that. Where do I start?

by pila Mon Aug 31, 2015 7:58 pm

Did you do the fuse removal test ? Some things are not fed (fused) through the fuse panel, like headlights.
Since the test light is cycling on & off, try pulling the turn & hazard blinker units off of the fuse panel.
Maybe a long shot, but worth a try.

Should be a silver colored circuit breaker plugged in the fuse panel also. Pull that also when checking with the test light.

by rogal_tx Tue Sep 01, 2015 7:35 am

Ok, turns out it was my aftermarket CD player, at least thats what it appears. When I disconnected power to it the light never came back on. CD player had led light that was blinking but that shouldn't drain the battery. Either way battery is charged and I will wait couple of days to see if anything have changed. Thanks everyone for your help.

by thatfnthing Tue Sep 01, 2015 8:42 am

Glad you found it.

The first thing I would check is if the CD player was wired per the diagram. It will likely need two hots -- one to preserve memory settings and one to run the actual unit. The first should be constant hot (i.e. even with the key off), but it will pull only a teeny-tiny amount of juice. The second, though, should only be hot with the key in On or Accessory. It will pull a LOT of juice, and could be the cause of your problem if it was accidentally wired as constant hot. Seen it happen before.

It's also possible something is actually wrong with the unit itself internally and it's pulling more juice than necessary.

by rogal_tx Tue Sep 01, 2015 9:46 am

I will look at the diagram today to see if thats the case. I was also thinking to install on/off switch for CD player but rather not do that.

by chevellelaguna Tue Sep 01, 2015 12:35 pm

That sounds about right. That light could draw as little as half an amp, that would be enough to drain the battery, I've had a half an amp short drain a brand new battery in a day. New cars cycle that thru the computer.

by thatfnthing Tue Sep 01, 2015 1:17 pm

LEDs don't use anywhere near half an amp. A typical automotive LED will draw about 15 mA, which is .015 of an amp, and you will die of old age before it drains the battery.

If the drain is indeed coming from the CD player, the blinking LED indicator is not your culprit. It's more likely an issue with the internal laser that is used to read the discs or the motor that spins them -- those draw a significant amount of juice.

by rogal_tx Wed Sep 02, 2015 7:41 am

Ok, radio is still disconnected, battery charged. I try to start it this morning and I heard a loud click coming from the starter and all the power got cut off. Had no lights ect.
So I moved the battery terminals and power came back on. Car started no problem but when I got to work parked it and try to start it again starter was draging turning over but it finally stared. I have remanufactured starter, is it possible for a starter to be causing all the issues with battery?

by Joe73 Wed Sep 02, 2015 7:59 am

Id highly doubt you have a starter issue if you moved the battery terminals and power came back on, I'd be looking at the battery terminal connections for issues.

by chevellelaguna Wed Sep 02, 2015 8:03 am

It's possible that something could be wrong internally with the starter. However your initial issue was with the battery. Have it tested, may have a bad cell. Not delivering enough amps to hit the starter.

by thatfnthing Wed Sep 02, 2015 8:48 am

Agreed. While it's 'possible' for something to go wrong with the starter electrically, it's unlikely. If you move the battery cables around and it works, I'd start at that end. Generally if you have to wiggle something electric to make it work, there's a loss of contact in there somewhere. Look for the most obvious causes: corrosion, loose or broken cable or clamp, frayed wire, etc. It's also possible the battery post is broken inside the battery and making intermittent contact internally, which you'll never find.

Do you have another battery you can test with? This would allow you to determine if it's actually the battery or the cable. And while you're at it, check for loose or corroded connection on the starter end.

by rogal_tx Wed Sep 02, 2015 9:39 am

I will check all that later today and post update on what I find.
Thx

by chevellelaguna Wed Sep 02, 2015 12:02 pm

Sometimes the ground cable was constructed of aluminum strands, could have been replaced at one time. Those are junk want to make sure you have a copper stranded positive and negative cables. Clean the grounds, have the battery tested.

by rogal_tx Wed Sep 02, 2015 11:04 pm

So I don't think it could get any worse: my starter failed and 4 month old battery was failing too. It was on last quarter of its life. Got lucky because had warranty on both of them. Replaced the starter, battery and it fires right up. Thanks for all the help from everyone.

by bigredlaguna Mon Apr 25, 2016 10:54 pm

Thanks to this thread, I was able to find the source of my battery drain. I really thought the problem was in the dash harness, because who has NOT has a rats nest. I had pulled all the fuses, disconnected all the switches, undid any stereo wiring, and I still had a leak.

Turns out it was the alternator that it was bad. I had never seen that problem before until reading about it here. I used the ohms setting and measured across the disconnected battery cables. It was always reading 5.42 ohms up to 5.9 ohms. That reading never changed until I pulled the 2-wire plug from the side of the alternator. Finally got an infinity reading.

Thank you thatfnthing, I never would have thought of testing the alternator.

by thatfnthing Tue Apr 26, 2016 9:27 am

Glad to be able to help!

by bigredlaguna Tue Apr 26, 2016 3:54 pm

Well, the new alternator does the same thing. Is there supposed to be a resistance reading between the red wire blade (in the alternator) and ground?

by bigredlaguna Tue Apr 26, 2016 5:14 pm

I checked my other car (the one in the avatar), for the same reading and it flashes to 19 ohms or so then goes to infinity immediately. Sucks when fresh parts are bad out of the box.

by thatfnthing Tue Apr 26, 2016 5:15 pm

The test for alternator drain is via amps, or failing that, volts. And it's off the main alternator feed, not the plug. That shows actual current flow in the wrong direction when the car is off. I can't speak to resistance on that circuit, either what it should be or if testing it that way would damage it and cause the very problem you're trying to detect. Some circuits are sensitive to that and some aren't. The alternator manufacturer would know best.

What do you get when you test it for amps/volts?

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