Very flat battery

[regtubby]

I've pulled an extremely flat battery out of the shed, showing just 2v of charge. It is less than 5 years old.

I'm tempted to put it on trickle charge for a good few days but I'd have to buy a charger (about £9), is that likely to be just good money down the drain and I'd be better off getting a new battery?

[Rob_Jennings]

a battery left uncharged is likely to suffer from frost damage (how long has it been there) and internal damage to the plates

I would invest in a new one personally.

[Kevin]

Once batteries get to 4 years old you are on borrowed time anyway and once thats not been used for a while is not going to be much use unlee it once a relly good one with a 4 year guarentee and even then I would go with Rob`s view.

[regtubby]

Much as I suspected.

And as if by magic Costco open in Sheffield today!

[Packedup]

Not sure if http://www.mztech.fsnet.co.uk/electrics/elc_edta.html is of any help?

Personally I'd try charging it, but not expect wonders:(

[blueangelical]

I'd go for a new one, even if it charges and does work, you never know how reliable it will be on those damp mornings. New ones hold a garauntee too......

[regtubby]

Damp mornings? I was planning on sticking it in the Trabi and using it in the desert.

[rayofleamington]

I'd buy a charger anyway! Tools are a valuable investment to last a lifetime....

As for the battery, you've not got anything to loose by leaving iot on charge for a week. It is unlikely to be any good but I've had some last 6 or 7 years. Even if it won't hold a charge very long it could keep a car running after you've jump/push started it

[Willie]

The worst thing you can do to a battery is to keep it in a discharged state!
A 12V battery consists of six 2volt cells connected in series so, if you charge up your problem item and read 12v minus increments of 2v then each missing 2 volts indicates a dead cell i.e. a reading of 10v means that one of
your cells is dead.

[Onne]

so it should read 12V all the time, just not be able to provide all the amps? Or am I wrong?

[Willie]

Good question after five years without charging!! once you have charged it
for a while it certainly should read minimum of 12v. You can get a good idea of its state when you use a decent charger as its gauge will read a high amperage at
the beginning but will gradually fall as the battery charges up, if it refuses to
fall below a certain level despite the fact that it is bubbling away merrily then the unit is in a poor state which,in your case, is highly likely I'm afraid.

[ColinP]

IF I remember correctly, a standard lead acid cell should have a voltage of 2.2 volts (in normal "good" condition.

Stack 6 cells together is series, and that's actually 6 x 2.2 = 13.2 volts.
10 volts hints that one cell is "dead" - 5 x 2.2 = 11 volts

That's why the regulator should "cut in" at 13.4v - the battery needs that little bit extra to push the charge into the battery.

As you take current (amps) from the battery, the voltage will fall. If you take lots of amps (say 50+ - like a starter motor), then the voltage across the battery will fall to 8-9 volts.
(back to Ohm's law - remembering that the battery itself has an internal resistance).

The best way of checking the charge state of the battery is with a hydrometer - this tells you the specific gravity of the electrolyte in each cell (and this identifies if there's one or more dead cells).

If you leave a battery discharged, the lead plates turn to lead sulfate (remember the electrolyte is sulfuric acid?). That stops the battery working and is just about irreversable....

Colin

[rayofleamington]

That stops the battery working and is just about irreversable....

True - but I've managed to get a bit more life out of a long term discharged battery by charging it for over a week. It will certainly not be a 'good' battery but depends what you want to do with it.
Does a Trabby have a starting handle? ;-)

Oh yes - a colleague saw this thread and commented that the battery is not 'flat' it is discharged

[lowedb]

If you leave a battery discharged, the lead plates turn to lead sulfate (remember the electrolyte is sulfuric acid?). That stops the battery working and is just about irreversable....

Very true. The other thing is that even if you manage to convert the lead sulphate back to lead, it ends up being quite flaxy, and can fall off (even if the sulphate hasn't already). When it does this it's very easy to end up with enough sat at the bottom of the battery to short out the plates and kill a cell.

True - but I've managed to get a bit more life out of a long term discharged battery by charging it for over a week. It will certainly not be a 'good' battery but depends what you want to do with it.

The problem is, that you can convert some of the suplhate back to lead, and the battery will take a charge, and give you a good voltage. The bits of the plate that you haven't cleaned up by charging (and may never recover) give you a reduced capacity, so it seems fine, but as soon as you need more than a couple of seconds cranking the battery will go flat very fast. You also get problems if the amount of sulphation varies from cell to cell, as the cells then end up with different capacities so some are discharged while others are healthy. This makes it harder to charge properly as you end up overcharging the good cells and undercharging the bad ones.

In answer to the original question, I would replace the battery. But I'd also get a decent (regulated) charger to keep it topped up when not in use.

[Willie]

As an aside to the above I read this week that modern batteries are being
produced with,of all things, glass fibre strands which do not deteriorate if left
uncharged for long periods! the technology is known as Absorbed Glass Mat
(AGM) and means that the battery is about 5Kg lighter,does not have to be
mounted on the flat,lasts longer and will not leak even if the casing is cracked. The VW Golf and Audi A3 are reported to have this type of battery
already. (Probably about £500 each)!!

[regtubby]

Well, I put it on charge for 24 hours and my multimeter is showing me that it has 13.14 volts.

No, the Trabi doesn't have a starting handle (not even a pull cord like a lawnmower before anyone gets in with that quip). It does have an electric hand warmer on the rear windscreen for when pushing the car in the winter and another nice touch is the light under the bonnet.

[lowedb]

As an aside to the above I read this week that modern batteries are being
produced with,of all things, glass fibre strands which do not deteriorate if left
uncharged for long periods! the technology is known as Absorbed Glass Mat
(AGM) and means that the battery is about 5Kg lighter,does not have to be
mounted on the flat,lasts longer and will not leak even if the casing is cracked. The VW Golf and Audi A3 are reported to have this type of battery
already. (Probably about £500 each)!!

Yes, we are using them too. It is still possible to damage them in the same way as older batteries, just a lot harder. The glass mat helps stopping the damage caused when the suplhate or flakes of reformed lead fall off, as the can't fall off. I'm not sure about mounting position, though. I thought it was only the gel electrolyte ones that could be mounted anyway you like. As for cost, yes they are more than 'normal' batteries, but are more common than you might think.

[Willie]

Regtubby, sounds good,but, as has been pointed out, you will probably find
that it doesn't produce the amperage of old. If you fit it on your car and have
a voltmeter across it when the starter is operated it would be interesting to
know what the voltage drops to.