Car battery being wierd...

[Bri957]

My project car has not been started for a couple of months.

The only obvious battery drain is a small red led, left over from a long abandoned alarm.

This had gone out, so I removed the battery for charging. It showed 1.8v on the multimeter. Plugged it into a smart charger, which wouldn’t come out of standby mode due to the low V reading. I left it in standby mode overnight and it increased to 2.8v.

Plugged it into a proper charger and it registered 8.9v after two minutes. 10.6 after four minutes, and 12.3v shortly after. This was all using multimeter readings.

Does this sound as though the battery is faulty. Can’t believe it can go from empty to full in under 10 minutes.

Grateful for any advice.

[liner33]

That battery is goosed , any car battery that's been down to 2.8v wont recover well

[Bri957]

Ah cool.

Annoying though, as it was new a year ago.

[liner33]

Might be worth putting a CTEK MXS 5.0 on it , will save the battery in future from going flat but might recover it enough

[Mr2Mike]

Bri957 said:

Plugged it into a proper charger and it registered 8.9v after two minutes. 10.6 after four minutes, and 12.3v shortly after. This was all using multimeter readings.

Does this sound as though the battery is faulty. Can’t believe it can go from empty to full in under 10 minutes.

12.3v is nowhere near "full" whilst the battery is charging. Depending on charge current that may only show 15-20% of full charge.

As liner33 says, discharging a battery that low will have damaged it. It might be recoverable to a useable state if you leave it on charge, though capacity and CCA will both have dropped, but it may also be scrap.

[E-bmw]

^^^^ Is the correct answer.

Had this some time ago & although it did last it was definitely down on power, as the car was never left for long after that it was OK though.

[GreenV8S]

The fact the voltage dropped that low suggests it's certainly damaged and probably scrap.

The fact it is not taking a charge indicates it's definitely scrap.

[Mr2Mike]

GreenV8S said:

The fact the voltage dropped that low suggests it's certainly damaged and probably scrap.

The fact it is not taking a charge indicates it's definitely scrap.

It sounds like it is taking some kind of charge using a simple 'dumb' charger, the voltage was simply too low for a 'smart' charger to recognise anything was connected.

[Bri957]

True, but for it to jump from 2.8v to 12v in ten minutes seems odd.

[finlo]

Bri957 said:

True, but for it to jump from 2.8v to 12v in ten minutes seems odd.

It's quite normal, its a ghost voltage that will drop straight back down if you try to apply any sort of load.

[GreenV8S]

Mr2Mike said:

It sounds like it is taking some kind of charge using a simple 'dumb' charger

If the voltage jumps up that quickly clearly the battery isn't actually taking any charge. Put a load across it and it will read as flat again.

[Bri957]

Ok - thanks chaps.

Will order a new battery and try and keep it topped up a bit more.

Cheers B