Flat battery, causes?

[croyde]

Went to use my car last night and it was completely dead, even the remote locking wouldn't work. I bought it 2 months ago and the original owner had just fitted a brand new heavy duty battery, the car is a Mercury Grand Marquis btw, and it has run like a train since.

Started every time and has been fine if left for 2 or 3 days, as I have another car and a bike. This time it had not been driven for at least a week.

Anything obvious I can check, once I have recharged the battery. I have a multimeter but no real idea how to use it or where as I have only just checked connections in the past.

What voltage should a healthy battery be showing when the engine is running and when the ignition is off and how can I check to see if anything is draining it?

There are no extras on the car that I know of, ie an alarm.

Cheers for any help.

[croyde]

Thanks mate, I'm just gonna take a good look. It was late and dark last night and I needed to get to my overnight shift.

Even wondering if I somehow ignored all the bonging and beeps and left the lights on

[croyde]

Thanks people. A lot of helpful suggestions unlike those jokers over on CrownVic.net where the best suggestion was use it more often then

Fine in the US where the petrol is cheap.

[croyde]

Just checked and no light switches left on and battery and it's terminals are clean and tight. In fact the engine bay looks almost new. It's a 14 year old car with only 32k miles on the clock and as said, it's a brand new battery.

[croyde]

Just going to check this now.

Got the car going but only by using the jump leads from my 'ol Beemer and jamming an umbrella between the drivers seat and the loud pedal to keep the revs high. Been for a drive and stopped and started it a couple of times with no problems.

The battery is a Yuasa which has a green indicator if charged or black if not. Currently black but the volt meter in my dash has the needle exactly between H and L.

I'll report back.

[croyde]

Thanks again guys.

After running the car for 20 mins with a 3 mile drive the battery is reading 13.75V with the motor running and 12.42V with the ignition off.

[croyde]

I will, ta.

Would not the low reading be down to the battery not being fully recharged by the short drive? Sorry if a daft question btw

[croyde]

Have been in contact with the previous owner who tells me he had the same problem from time to time, thus bought the new battery just before he sold it thinking the old one was duff.

Using the car everyday was fine but if he left it a week the battery died.

So I'm thinking the previous answers saying a battery drain are the correct ones. Can anyone tell a numpty like me how to use the multimeter to test the fuses to try and narrow down the culprit.

Like where exactly do I stick the prongs and what readings to look for

[croyde]

Ozzie Osmond said:

If that 12.42 is immediately after switch-off and read with a good voltmeter you've almost certainly got a duff battery. Let it stand overnight and check it again tomorrow before you start the car. I'd be interested to know where the voltage lands.

12.14v this morning ignition off.

[croyde]

Same question about the stereo as the previous owner took out the oem Ford cassette player and installed an all singing and dancing cd usb bluetooth Sony tuner.

It turns off with the ignition but surely there is a constant live feed so it can remember all its settings.

[croyde]

Just to add this to the mix, the boys over at CrownVic.net all have 850 amp batteries whilst the one fitted to mine is only 650 amps. Could this be the problem or just adding to it?

If you go on a US car battery site, they also say the battery should be 850 amps.

Thanks.

[croyde]

Matt_N said:

Yep the stereo will have a permanent live (for memory settings) and a switched live (for powering on).

Would this be enough to drain the battery slowly say over a week. How do cars with modern stereos manage?

My '98 BMW has a modern stereo with iPod and all sorts of settings yet I can leave it for weeks yet it still starts.