Battery Issues - advice needed

BigT · 3 Dec 2012 at 18:55

So I fear my beloved old jeep may be terminally ill.

Six months ago I left the lights on and knackered the battery as a result. It was of an unknown vintage and looked very old so replacing it with a shiny new one wasn't too unexpected.

Fast forward to early last week and having attempted to start the car, not a sausage. I still had my jump starter from earlier in the year and she fired up. An hour's drive to work and that evening she started fine on her own. Cue a week of normal use every day and I just put it down to one of those things.

This evening I go to start the car and again not a peep, light or any signs of life. I jumped it again and drove home, about an hour's journey. Once back I turned her off and this time immediately everything went dark. No juice to turn on an interior light, let alone start it. I brought down a voltmeter and ran it across the battery with everything off. Not a single Volt.

So I ask motors what might the prognosis be? Seems odd for a battery to be shagged so quickly from new. The first episode last week didn't seem to be caused by leaving anything on so perhaps something causing a drain somewhere? But then why wouldn't it have got any charge on the way home?

Any advice gratefully received before I take it to the local mechanic.

Zack101 · 3 Dec 2012 at 20:04

Be very unusual to have nothing in the battery, what's it charging at?

Fuzz · 3 Dec 2012 at 20:26

Jump start it, leave it running... What's the voltage

Take battery off car, charge over night, allow an hour for "surface charge" to dissipate and then test the charge level. (drop test)

Let us know the results.

BigT · 3 Dec 2012 at 20:40

Zack101 said:
Be very unusual to have nothing in the battery, what's it charging at?

Forgive my ignorance, but how do I know what it's charging at? While driving the in car gauge showed just under 14V but turned it off and battery dead. When I say nothing, my portable meter gave a little wobble to acknowledge it was at least connected to something!

Fuzz said:
Jump start it, leave it running... What's the voltage

Take battery off car, charge over night, allow an hour for "surface charge" to dissipate and then test the charge level. (drop test)

Let us know the results.

Thanks, I'll try that. As above, when I jumped it and set off the in car gauge showed 14v all the way home, but I'll try just starting it and leaving it running for an hour without driving as you suggest and take a reading.

I'll also get it off the car and do the drop test as you suggest and post back.

Thanks both.

Zack101 · 3 Dec 2012 at 20:47

14 volts is about right, do you trust your volt meter? As above if you have the car running and put your volt meter across the battery, the reading is what it's charging at. 13.8 volts is ideal but anywhere around 14 is ok.

BigT · 4 Dec 2012 at 16:38

Fuzz said:
Jump start it, leave it running... What's the voltage

So this mornign I started it. For the first time ever the engine died after starting, necessitating me to give it some revs in neutral to keep it running. After two minutes at 1.5K rpm with ym foot on the gas it would then idle fine.

I left it for an hour running at idle. Voltage throughout on the car's meter showed just under 14V and on my portable meter across the terminals was showing off the scale (it only goes up to 12V).

Turned it off after an hour of running and everything was dead again. 0V registering on the portable volt meter and in car.

I suspect the battery is now shagged as they're not supposed to be allowed to completely discharge, right? I'll perform the "drop test" as suggested anyway.

Fuzz · 4 Dec 2012 at 17:23

Good start, looks like the alternator is charging ok at least.

Dogbreath · 4 Dec 2012 at 17:57

Sounds like one of the cells has gone open, which is a relatively unusual failure but not unheard of. Can you see the electrolyte level through the casing? If so, so all cells have approximately the same level?

Clarkey · 4 Dec 2012 at 18:01

Must be something like that ^^

I've had loads of dead batteries in my time, even the flattest of the flat still reads 6V in my experience.

Zack101 · 4 Dec 2012 at 18:11

This is very strange, a fully charged battery even if it's dead should read 10 volts. I have never known a battery to read zero volts, not one that's been in use anyway. Do you have a trickle charger? If so take it off and charge it then see what happens.

It is possible for the alternator to show 14 volts and still be faulty. Charging the battery off the car will tell you if that's the case here.