Alarm goes off when I disconnect the battery!

Asked by Apr 06, 2015 at 07:38 AM about the 2000 Volkswagen Passat GLS

Question type: Maintenance & Repair

I went on vacation for 6 weeks and when I returned the battery was drained. I charged it and everything was fine. I am leaving again on a long vacation and thought I would disconnect the battery to avoid the problem on my return, but when I disconnect the battery cable the alarm goes off.

6 Answers

4,515

Put your key in the ignition, turn to accessory, and then connect the battery. Should be okay.

Thanks Scott but I want to disconnect the battery as it drains when I am away for more than 4 weeks. The problem is when I remove the battery cables, the alarm goes off. This seems strange unless the alarm has another power source. A related question if I keep charging the battery every time it drains, does it reduce the life of the battery?

4,515

If you remove the battery positive cable while the key is in the ignition (off) it may defeat the alarm. The alarm may be able to function after the battery is disconnected due to stored energy in it's system, capacitive or battery. BTW, if you have a slow drain you should locate it...or install a trickle-charger to maintain the battery for long duration parkings.

1 out of 1 people think this is helpful.

Thanks Scot. How can I find out if there is a slow drain and how can I locate it? The alarm is certainly using the battery and I also notice that the LCD display of the clock and mileage indicators are on when the ignition is off.

4,515

The LCDs draw only a few milliamps...no worry there. As an electronics tech, I have used a clamp on ammeter to measure the current through the primary positive lead to the fuse box while the vehicle is off. Then, systematically, pulled a fuse for a circuit, checked the reading, replaced the fuse and moved on to the next circuit. It is tedious but effective. You can also obtain a solar charger identical to what the dealers use. It connects to the OBDII port and can be placed on the dash or window to provide a maintenance charge.

2 out of 2 people think this is helpful.
4,515

Automotive batteries are not like lithium ION batteries in portable devices. They have lead plates and electrolytic fluid that react chemically to store and discharge electrons. These lead-acid batteries typically last 5 years or more. The standard (un-sealed) lead-acid batteries can be reconditioned by replacing the electrolytic fluid. It may be you simply have a tired battery...

1 out of 1 people think this is helpful.

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