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So i have this problem. My passat keeps draining battery. SO i changed the battery and poof drained . Its like something its eating the power. Where to check? Someone with same problem?
 

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i would check the alternator. Without it, the car has no way to recharge the battery, so even a new battery would die pretty quickly.
 

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Don't overlook the obvious. The girlfriend's old Acura would drain it's battery in a day or two, and the dealer couldn't find the trouble. Turned out the switch on the trunk light was sticking. I've also seen more than one person with an aftermarket stereo, where the external amp wasn't shutting off automatically the was it was supposed to.

Finally, just because a component (battery, alternator) is new doesn't mean it's not defective.
 

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If you run errands on your day off and you start and stop the engine a few times, does it sound the same when it's cranking after the fourth or fifth time? If it starts to sound drained, you're not getting a charge. I'm with Axle on this one and would be looking at the alternator first.
 

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disconnect your negative terminal from the battery, connect a tester in between(regular light bulb tester) if it glows bright start taking fuses out one by one, until the light goes out. and that would be the problematic system. make sure to engage the door lock so the micro switch don try to turn the light on, and don't forget to disengage it before closing the door. the only system that should drain the battery a very little is your radio but the light should be very dim at that point, and make sure everything is off in the car at the test time...
good luck
 

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put the negative side of the volt meter to your battery's negative and the positive to battery's positive, start the car and see what it says, it should be more than 14v
 

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jip. get a multimeter.

check for 13.8volts plus while running - this would indicate charge from the alternator - the voltage is constant and rpm shouldn't affect it.

when the car is off use an ammeter on the battery to check current usage. remember to switch off standard stuff like lights, interior lights etc.
pull one fuse at a time and check for current drop.
you then know what system is using the current and can then try and figure out what the specifics are

Usually drainers are
- phone kits
- stereos
- aftermarket amps not switching properly
- boot light
- aftermarket immobilisers
- tracking systems
 

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When you remove the key, are you getting a clunk and power accessories are turning off? It might be acting like the key is still in which will keep the CCM powered. Learned this the hard way by shutting off and not removing key. Killed the battery in one evening
 

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What is a reasonable time for the battery to drain, simply by not driving the car for a while? The reason I'm asking is because I've just had to jump start mine this morning because the battery was drained after about 3 weeks of the car being sat out side (except for about two or three short trips less than six miles in that period.

I've checked the glovebox light and boot light but they're off. I do have a permanent live feed to the stereo so that when its off it sits on standby so that the memory in the stereo isn't erased.

My battery is only 18 months old, the old one lasted for over 4 years and I had no problems and I often left the car standing for a week or so without driving it.
 

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bump for a response to the above?
OK, not necessarily a good response, but a response: "It depends." Each car will have a different parasitic drain, each battery will have a slightly different self-discharge curve. (Though for lead-acid batteries it's generally pretty shallow). Climate affects it, too.

The girlfriends 2009 Acura MDX (which has the Technology Package, and I suspect a rather high idle drain) seems to go from fully-charged to starter-won't-engage in 4 weeks or so. My 2000 GLS (with a venerable DieHard) got balky after my periodic 10-14 day trip to California.

If you make short, low-speed trips in between, it makes it worse - the alternator doesn't have time to replace what the starter uses. (You learn a lot about this if you've ever owned a Diesel car with glow plugs).

Executive summary - my guess is, a B5/5.5 with a reasonable battery and no wiring problems should have no problems with a month idle. To be on the safe side, I always "exercise" mine after no more than two weeks.
 

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If everything is wired properly in your car you should be able to have it sit around for a coupple months and still be able to start it.
Problems arise when aftermarket things are installed incorrectly, or a wire somewhere gets scuffed to the point where the bare wire can touch metal and then puts a constant drain on your battery by being shorted out. Had this happen with the trunk wires in a passat.
But use the instructions above to troubleshoot, check if you have a drain, just make sure you check the obvious first before you go hunting for wires that might have gotten jambed and scuffed. Obvious things, intirior lights, glove box and trunk underhood lights etc.
Good luck with the search
 

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2001 b5.5, the 6 cd changer in the back is a common drain, if left on obviously, or fuses. i also had a battery drain every few days and didnt know what it could be. took the cd changer out, and it has been fine since. just my 2 cents
 
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