dead battery?

Does the charger give a current reading? 4A for around 90 hours suggests 25% efficiency, which doesn't sound so bad. Unless it's a fancy constant-current charger, you may not be pumping in half that current, so I don't see anything to worry about.

I'd check the charge with an hydrometer, myself.

On or around Tue, 18 Jan 2005 11:49:35 +0000, Mr.Nice. enlightened us thusly:

measure the voltage, disconnect the charger, measure the voltage, wait an hour or so, measure the voltage.

about 14V, 13.5V, 12.8V or so, I should think.

if you get 14V, 13V, 10V then it's shagged.

I'd best go and buy a new battery for my multimeter then, I nicked the last one for the smoke alarm...

Regards. Mark.(AKA, Mr.Nice.)

Could be or maybe it just needs a bit of a blast to destroy any crystals that are shorting the plates, though it's never really going to fully recover.

What is the terminal voltage under load of an amp or so? (12v 15W bulb or similar) if it's not pretty close to and steady at 12v then you have lost at least one cell.

I've had a couple of batteries so flat that I couldn't trickle charge them - they just sat 'charging' forever'. I bolted them into the 101 in the secondary position and let that 'quick charge' them for a short while - 5 minutes or so. Back on the trickle charger and good as gold....

Those were starter batteries, not leisure ones, though I guess the same would be worth a try if the option is to bin them. You will need a 101 of course...

with the charger on 'normal' which I'm guessing is 4 amps - 13.81 volts with the charger on 'fast' which I'm guessing is 8 amps - 14.05 volts. charger off - 13.78 volts.

30 minutes later - 13.57 volts.

Regards. Mark.(AKA, Mr.Nice.)

The charger just has 3 led's on the front and the amount of light from them hadn't changed.

Regards. Mark.(AKA, Mr.Nice.)

Check out

It tells you more than you will ever need to know about all types of batteries, how to charge them, how to discharge them, what the chemical makeup is and loads more.

It reckons that you should not let lead acid batts fall below 2.1V per cell (12.6V) in an ideal world.

Sounds knackered to me. I had a car battery that went flat after being left and it was never right afterwards, it did like you describe.

Seems a healthy enough off load voltage. Try bunging a bit of load, that 15W bulb again (indicator or similar) on it and see what happens. Small drop OK but more than about a volt isn't so good.

and a couple of hours later down to 13.31. not sure I like the idea of it dropping with no load on it. but then I suppose that the rate it's dropping would not be a problem as I plan to use it on a split-charge to run aux lights, charge torches, camera batteries, laptop etc.

Regards. Mark.(AKA, Mr.Nice.)

That's the float charge being dissipated. Once it's fully dissipated it should drop to approx 12.6v when fully charged - the quickest way to remove the float charge is to draw about 10 amps out for a couple of minutes then leave the battery to stand for half an hour or so before testing.

After dissipating the float charge at 20 degrees C fully charged will be about 12.62v, half charged about 12.0v and dead flat about 11.62v.

HTH

On or around Wed, 19 Jan 2005 08:34:24 +1300, EMB enlightened us thusly:

mind, the heavy-discharge tests for the rated starting current run the thing down to about 1.2 or 1.4 V per cell, for a total voltage about 8V...

but yeah, anything substantially below 12V after it's been sitting for a few hours is not good.

The one under discussion sounds OK, though. Of course, the electrolyte level's been checked... ?

I once got a free battery that way. Someone had dumped it in a car park - I found it, looked at it and noted only about an inch of electrolyte in each cell. Took it home, filled it up with distilled water, charged it, and it ran the car for about a year and was still on the car when I sold it.

Yep the electrolite is all fine, I'll bring a bulb along tonight and try it with a bit of load. If it looks OK I'll put it on an 8amp charge and see how it goes.

Regards. Mark.(AKA, Mr.Nice.)

One thing you should recognise is that the rated charge of the charger is not likely to be what it is actually charging at - so it is probably not had as much charge as you think it has. Most chargers drop the current well below the rated charge as the voltage rises. For example, I have at present an 8amp charger on a 760AH battery - at 13.6 volts, the charger is only delivering about 1.8Amps. On a fully charged, good, battery the voltage will be around 14v at full charge while charging at 5-10% of rated capacity, but with the charging stopped will drop to 13.2 volts with no current draw. What it drops to under load will depend on the load, but again, with around 5-10% of the rated capacity load, it should remain around 12-12.5V and drop only slowly until about half discharged. JD

On or around Wed, 19 Jan 2005 20:18:25 +1100, JD enlightened us thusly:

wot's it for, a submarine?

I think you're confusing AH with cranking current.

760 Ah would let you draw 760 amps for an hour, which is a pretty damned big battery!

Main house power supply. My house is supplied by two 24v 760AH and one 12v

400AH battery banks charged by twenty solar panels and running three inverters. I got a number of second hand spare cells, and the set referred to is getting a maintaining charge.

I assure you I know the difference between cranking amps and AH. The cells in question would not have a "cranking" current more than about 150A, as they are, of course, deep cycle cells. JD

On or around Thu, 20 Jan 2005 06:54:48 +1100, JD enlightened us thusly:

fair enough. I sit corrected. Bet you could run a submarine on 'em, an' all.