Dead battery after ten days???!!!

I had put my car ('03 Jetta TDI wagon) in the garage on Sunday, Feb. 22. The doors were unlocked and the alarm was not armed. I went out to start it today, and NOTHING! The clock and odometer/trip odometer were blank, and the interior lights did not come on when I opened the door (the radio did not go to SAFE). No dash lights came on when I turned on the ignition. I charged the battery enough to get it started and took it out for a ride; it starts fine now.
My question is this: is it normal for the battery to go dead like that after less than 2 weeks of not driving it? Also, did I do any permanent damage by running the battery down that far?

You should definitely charge the battery all the way up with an external battery charger.

I don't believe the battery will get fully recharged with just the alternator. It may also be hard on the alternator. I had a Suzuki GS850 motorcycle that fried the alternator when I rode it a while after the battery had partly self-discharged pver the winter. The guy at the shop asked if I had a trickle charger and when I replied no he said that was the problem.

The alternator is meant to keep the battery topped off and handle the load under normal conditions.

But... I have left my car at the airport on numerous occasions for 10 days or more and never had that happen. I still have the original battery after 3.5 years and 52,000+ miles.

Something drained your battery. Now you (or if the car is still under warranty, the dealer) need to figure out what did it.

An interior light may be the culprit. My son managed to kill the battery in our Jeep once that way and my wife did it again a couple of weeks ago on a business trip. A rear "reading" light was once left on overnight in the Jetta although the car started fine after that incident. But I would think it could be enough to kill it in 10 days.

Good luck.

If the car was unlocked and the alarm not activated, I believe the electronics will not go into 'low-power' mode. This means that the so-called 'parasitic' drain of all the electronics will be at its highest, the equivalent of leaving on a dome light. After two weeks, dead battery.

If you do this alot, I suggest getting a solar charger to keep the battery up.

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If the car was unlocked and the alarm not activated, I believe the electronics will not go into 'low-power' mode. This means that the so-called 'parasitic' drain of all the electronics will be at its highest, the equivalent of leaving on a dome light. After two weeks, dead battery.

If you do this alot, I suggest getting a solar charger to keep the battery up.

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I thought it was the opposite!!! That If you locked the car, arming the alarm caused MORE current drain! That's why I left it unlocked in the garage. If I'd have known that, I definitely would have locked it! After I got the charger hooked up to the battery, I checked all of the interior lights; none had been inadvertently left on. I fold the rear seats down a lot to put my bike inside; I'm always hitting the ones in the back with my head, and turning them on... /images/graemlins/rolleyes.gif
I do have the solar charger; I didn't put it in because there wouldn't have been enough light in the garage for it to work. If I do this in the future, I'll put the battery charger on it and leave it on trickle charge!

Just want to clear up a misconception about alternators and power output. Your alternator IS designed to dump tons of current into a battery - haven't checked specifics on our TDI's but the old Bosch alternator of the A2 variety put out 100 amps - Much more than a trickle charger can put out. Charging the battery by driving car is fine - no harm/no foul.

On the root cause of the dead battery - does sound like a light may have been left on - by any chance was the trunk lid not latched?

Timbo

I believe our (A4) alternators are different than those of old! They have energy efficient "shedding" alternators which switch on and off like an A/C compressor. They are designed to just keep up with current useage and keep the battery topped off. I am not an expert on the new ones - just repeating what I have heard. Maybe someone who has knowledge of them can pitch in.

Last summer, I left my 2001 Golf GL TDI in a parking lot at work for 60 days with the doors locked. When I returned, it started right up. I left it for 30 days, doors locked, in a cold Maine winter (January 2004, temps went down to -20F at times). It also started right up when I got back.
Original Battery.

All modern (since last 30 years) alternators have a built in voltage regulator switch. This is a solid state system which regulates the amount of current flowing from the alternator. You are correct that they just "top off" battery and do not overcharge the system, but they do this by sensing the electrical load on the entire system. If the battery is charging, it senses that load and boosts output accordingly - when electrical load decreases (battery topped off, defogger turned off, etc.), the system voltage rises, and the alternator cuts down output to match new load. There are no fundamental differences between electrical systems between A1 through A4 VW's. Only difference is the maximum output of the various alternators depending on system design load.

Look it up in your Bentley Manual - explained pretty well there.

Timbo

I'd have to say it's not ABNORMAL, but then agian also not desirable. Out of 5 cars, several of them sit for long periods of time. I only keep batteries in 2 of them, one which is daily driven, and the other I start... once in a while. I've let the other go for as long as 2 months without starting, and the battery was still just fine. Fired right up w/o a boost. However, running down the battery like that is just bad for it unless you have a deep cycle battery like an Optima yellow top. Starter batteries have smaller lead cells that break down quicker when run down to low voltage. This is why batteries die if discharged often.