Battery seeming to drain overnight

I have a '97 VW Golf TDI estate. The car has always started like a champ, but recently it's started becoming reluctant to turn over in the mornings or if I've left it for a day or so. I work as a delivery driver and stop-start my car 30+ times a night with the headlights and stereo and often the wipers on, so obviously the starting and charging system takes a bit of a hammering. I'm fairly certain the alternator is good, as it'll start instantly throughout the night at work, and my meter shows 14.4v at idle. This leads me to believe that the battery is on the way out.

I've checked for possible drain by removing the negative terminal and placing my meter set to the amps mode between the battery and the negative terminal. Even with it set to the lowest sensitivity it shows zero. I don't know if that means I did it wrong (does it need to be off the positive side? I didn't think it made a difference?) or that the normal drains (stereo clock and cluster clock) are simply too small to show up. Hopefully it's the latter and I don't have an errant drain I need to track down.

Does this sound like a bad battery? If so I can go pick one up and carry on with my life. I don't have money to burn on replacing the wrong thing though.

Edit: Something possibly related, but not entirely, is that if I leave the ignition on with the engine off, the battery will be too drained to start the car within five minutes. I've simply avoided leaving the ignition on because the key sensor in the ignition barrel allows me to have the radio one with the ignition off, so I have no need for it, but I imagine this is a problem that will probably need solving at some point. FWIW, the radio will happily play for 30-60 minutes and the car will start easily. Someone I work with suggested it might be a sticky glow-plug relay, but I'm not entirely sure. I never use the glow plugs.

Also, with the engine off, the battery sits at 11.8-11.9V. Is this too low?

Thanks!

Fully charged battery would show about 12.7v. 11.8-11.9 is way too low, battery is almost empty.

I think there is two scenarios: battery is dead or there is somewhere massive current leak.

Tureq said:

Fully charged battery would show about 12.7v. 11.8-11.9 is way too low, battery is almost empty.
I think there is two scenarios: battery is dead or there is somewhere massive current leak.

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I took the reading of 11.9V less than a minute after I stopped the engine. Time for a new battery then?

CameraJack said:

I took the reading of 11.9V less than a minute after I stopped the engine. Time for a new battery then?

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It's either toast or the alternator isn't charging, but then the battery would eventually be completely dead. Sounds like one dead cell in the battery. You should have almost 13 volts right after shutting down and around 14 volts when running.
The low voltage only tells part of the story. With a dead cell there is a big amperage drop when you go to crank it. I suspect under a load test the battery will fall completely flat.

jettawreck said:

It's either toast or the alternator isn't charging, but then the battery would eventually be completely dead. Sounds like one dead cell in the battery. You should have almost 13 volts right after shutting down and around 14 volts when running.
The low voltage only tells part of the story. With a dead cell there is a big amperage drop when you go to crank it. I suspect under a load test the battery will fall completely flat.

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As I said in the post, right after starting when running at idle it's giving me 14.4V so I'm pretty certain the alternator is doing it's job. Some mornings it'll barely turn the engine over before just about getting it to start. Once the car's been started that day, however, it'll bump itself into life without even straining.

CameraJack said:

As I said in the post, right after starting when running at idle it's giving me 14.4V so I'm pretty certain the alternator is doing it's job. Some mornings it'll barely turn the engine over before just about getting it to start. Once the car's been started that day, however, it'll bump itself into life without even straining.

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I chased a battery drain in my Suburban all fall after deciding it wasn't a bad battery after a new one and a swap with an existing one that was known good. It would last for a week or so sometimes more/less depending on the temps, etc. Thought it was the glove box light. Nope. Had the alt tested. Nope. Finally found one of the vanity mirror lights in the drivers side visor had a broken hinge and it was on the switch side so it never shut off even when it's cover was down/closed. Even looked it all over at night, but because the way it seals up you couldn't see any light.
If yours is loosing it overnight there is something more drawing it down. Stereo w/amp that doesn't shut off perhaps? Trunk light, glovebox light, etc shouldn't really be that large of a draw to good diesel battery.
Load test that battery, I think it will fail.

You didn't mention the age of the battery.
And the specs...
Amp hours:
Reserve minutes:
Cold cranking amps:

Did you take off the terminals and clean them?
As a diagnosis could you swap batteries with another car for a day or two?
You could do a load test yourself.
After driving the car for a while turn it off and take a voltage reading.
It should be close to 13 volts.
Then with the engine off turn on head lights, and heater fan on high.
Connect meter and watch the voltage.
It should be very slow to drop.
In five minutes it should still be above 12 volts.
If it falls fast to under 12 volts, then the battery is bad.

Please post your outcome.
Thanks

CameraJack said:

I took the reading of 11.9V less than a minute after I stopped the engine. Time for a new battery then?

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Definitely. As stated above, the battery voltage right after shutdown should measure a little (up to 13.0 v IMO) over 12.6, then settle to 12.6v some period of time after sitting. That period could be multiple hours long, but probably not more than an hour.

I think the behavior you are seeing indicates a very weak battery that is doing OK right after charging. 14.4 v while running should be providing good charging amperage. And leaving the ignition on will drain the battery rapidly, whether you are running the glow plugs or not (i.e. whether the glow plug relay is working properly or not).

Make sure you get a battery that is up to the task. 80Ah capacity is the OEM battery size. If you can't find that, get one with a reserve capacity of at least 140 minutes. But since you are on that side of the pond, I think you'll be fine with the DIN specifications.

Cheers,

PH

Its important to get this replaced as your alternator is working extra hard to make up for the bad battery. At some point you'll kill the alternator...