i was gone for a few days at the USGP and when i got back, my battery was dead. i have a new alternator that has worked great and tests as working yet the battery was dead. i jump started the car yesterday and it started up right away.

does anyone have any idea what would cause this? i've had to replace (on autozone's dime) my battery 4 times in the past 18 months for this problem.

 

ok, let me rephrase this... anyone have any hints on how to track down shorts in the electrical system that may cause the battery to drain?

 

Well in theory..I'm just going off general electric theory here - you want to put an amp meter in-line between the battery and all possible car systems. While ideally when the car is 'off' the flow should be zero, presumable you are going to measure some flow out of the battery. Should there be any? Well a stereo might draw a little, and I know my clock is always running.

If you eliminate these two drains by disconnecting them and the flow is not zero, you need to find where it is going. I'd start by pulling the hot fuses one at a time; and if I could localize to a fuse, then pull the connections that are on that circuit.

Kind of brute force but I think I'd get there.

Anyone have a better method or know why this won't work?

 

The fastest/easiest way is to get a current meter and hang it off the positive battery cable. This will indicate the amount of the draw. Now, start pulling fuses/disconnecting things until the current drops to 0. Now you've found your culprit (or have at least narrowed it down). This kind of work can be long and tedious.

http://www.thetoolwarehouse.net/shop/AMP-ACD6TRMS.html

 

yep - like I said

but you can get away with a MUCH less expensive meter too...may not be totally accurate but you are looking for zero vs anything rather than accurate AMP. But don't just use a light bulb! I still use an old analog volt ohm I've had for 30 years and I think was a freebe from Radio Shack! It has 'hark' a needle that swings on a scale .. not a digital readout!

p.s. - since most time the 'appliance' - say the headlight, gets no current if the switch is off. It would seem logical that the drain would occur at a bad switch. Something that's not fully off....perhaps a switch, or a relay got some water in it. Which also makes me think: have you added anything electrical? New or replaced wiring????

And here's a wild thought. What's the condition of your battery cover? I had the orginal fiber board sort of box top that fit as a cap over the battery. I noticed that mine had absorbed moisture over the years. When fit into place it contacted the battery posts. Damp cardboard is a conductor....I found a piece of tupperware that was the right size to serve as a battery cap after a little trimming. It hides under the boot carpet, completely out of site but provides complete insulation to the bat' terminals. Is it possible that when everything is buttoned up, you are actually placing a poor conductor across the terminals??? I don't know if it made a difference you not.....but I did occasionally have a weak crank b4 I did this....even with a new Red Top... No more..

 

a single bad diode in a lucas alternator can cause lower power to drain back thru the ignition circuit. Are you sure that the charge light isn't on ever so faintly? Had this happen on an MGB & could hardly see the lamp on.

 

ok, stupid question here... where's the charge light? my alternator is brand new (well, brand new rebuilt).



my batter cover is brand new and not wet.

i'll also run out and get a current meter or something like it (not a bulb).

 

he means the red light on the speedo - that's the ingition system/charge lite. Sometimes this can be on but very very dim.

Yep, I remember now that you just changed your alt' (about same time I had to do mine!) so I doubt that's your problem, but you might want to take a real close look at the electrical connection anyway..... Nothing got amis when you pulled the plug on the old alt' and stuck it into the new, did it?

Any you are sure the battery is holding a charge right? Was this an unusually long time 'tween starts. By that, I don't mean was it months as obvsly 'twas not. But do you generally start every 3 days and this time it was 14 days? In which case your battery just may be bad.

I had a cheapo battery in mine when I bought it. Brand new - but a cheapo. After 1 year the battery wouldn't hold enough charge to start the car for more than 7 days. No drain anywhere - just a crap battery. It would take a charge just fine...but be dead in 10 days.

A new battery - a good battery - solved that one. Took the crud battery to AutoZone - where it came from, and said it seemed like the bat' ran down fast - and they said, "did it hold up for more that a year?" yes "better than average." It was the cheapest battery they sold. Replaced with an OPTIMA and have never had a problem since. Funny thing was the cheapo would go thru the tester OK ... it just wouldn't hold a charge. Fact that AZ keeps giving you new battery tells me you need something better - like I did.