Battery reads 900 V !!!

[Pascal]

Hi,

After neglecting my moggy for 6 months I went to start it and not surprisingly found the battery very weak. The ceiling light hardly lit. I took the battery off the car, plugged my auto charger but the latter only applied the trickle charge. I left it that way for 24 hours, and when I unplugged the charger the battery read 900 V ! After a few hours it was down to 850 V, and after a few days down to 12 V. I put in on charge again and it went again to 900 V.

Any idea to what might be happening ? Is it definitely fried ?

Cheers,
Pascal

[bmcecosse]

I suggest 900 mV - certainly not 900 volts. A trickle charger will never shift it - in fact - safe to say it is knackered. Treat yourself to a new battery - and a solar charger to keep the battery up when the car is not in use. Of course the solar charger needs to be mounted facing south, and angled to take best advantage of the low winter sun. Maplin had them on sale for < £10. It works !!

[Pascal]

Well it´s definitely 900 V. The voltmeter went mad and I had to switch it the 1000 V DC scale to get a reading.

The solar charger wouldn ´t help much in my underground car park I guess...

[beero]

I think your voltmeter must be faulty. There is no way a car battery could give out 900v.

[MarkyB]

It's toast, the meter is little better.
If you can't rig up a solar charger the next best thing is to disconnect the battery when not in use.
Leaving a battery dead flat is the fast way to ruin, I've knackered enough motorbike batteries to have learned this lesson.

[mike.perry]

900V would fry everything including the house electrics and blown the fuse or circuit breaker

[lambrettalad]

900 volts sounds like A POP SONG ,no way in a moggie,impossible

[bmcecosse]

It will also kill you - stand away from the car.............

[smithskids]

Maybe the switch on the AVOMeter has slipped.

[katy]

Maybe the decimal point doesn't work, or maybe he didn't see it.

[Pascal]

Well I've spoken to a battery specialist who said that such a high voltage can happen if there is a broken/faulty plate in the battery. The broken plate has very high electrical resistance, which causes the current to drop and voltage to rise. So even if it amounts to a few hundred volts the voltage will drop to a few volts as soon as the battery tries to power anything as small as a light bulb.

In any case the battery is pretty well fried and unrecoverable.

Cheers,
Pascal

[MarkyB]

That explains it then, no way it could have been a true reading.
" You canna change the laws of physics captain!"

[bmcecosse]

I don't think I have ever read such utter rubbish in all my life before......... 'battery specialist' !!!!!!!!!! Aye right....

[rayofleamington]

Ditto - the battery specialist didn't study any chemistry?

It will also kill you - stand away from the car............

Yes - a genuine 900v DC is rather lethal. It only takes 20 milli amps across your chest to stop your heart.
The capacitive level of a lead acid battery at 900v would be a very dangerous thing - fortunately it' also pretty unlikely based on the laws of chemistry that it was anything like that.