Lead acid battery mystery.

I have a number of used but still functional car batteries which I use for electric fencers and lighting at a stables with no power.
Some are sealed, but for the ones with removable caps I always remove the cap and check the acid level before putting them on the charger.
I have just one battery which always has low fluid in every cell when I bring it back for recharge. It takes an exceptional amount of demin water each time, at least 50 ml per cell if not more. All the cells are similar. But, when recharged, it reaches a reasonable voltage and certainly holds a useful amount of charge.
The cells can't be leaking significantly, firstly there is no sign of it and secondly this must have done a dozen cycles like this over the past year or two. I havn't actually checked the acid concentration, I probably should, and top it up if necessary.
Does anyone have an explanation?
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On 17/11/17 17:18, newshound wrote:

internal short maybe on that cell
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On 17/11/2017 17:23, The Natural Philosopher wrote:

But it is *every* cell, and it does hold a reasonable amount of charge.
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No he says all the cells and the way to see the short would be to just leave it in a cool place for a while without using it. Brian
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On 17/11/2017 17:18, newshound wrote:

Do you do a similar check after it has been charged?
I would expect any water usage would be in the charge cycle.
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On 17/11/2017 18:02, Fredxxx wrote:

Yes, so would I. I stop charging when all the cells are fizzing nicely and don't normally have to top up again at that stage.
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On 17/11/2017 18:17, newshound wrote:

The fizzing sounds an issue. You ought not allow the battery voltage to be high enough for cells to 'fizz'. A short equalisation charge is all that is needed. What is the charge end current?
What do you mean by 'normally'? Perhaps gas on the plates is raising the level such that after charge it looks ok. I would check sometime after you've completed the charge process.
Next question! Do these batteries get much movement? I have heard of electrolyte stratification being an issue that promotes gassing.
Have you checked the electrolyte density of this battery?
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<snip> >The fizzing sounds an issue. You ought not allow the battery voltage to

If we are talking about 'gassing' here then isn't it actually *required* as part of the charge process of a flooded lead acid battery to prevent electrolyte (and so charge) stratification?
http://batteryuniversity.com/learn/article/water_loss_acid_stratification_and_surface_charge

I think the second part of your question may answer the first part. ;-)
The 'equalisation stage' duration would (of course) be a function of the (bulk) charge rate and / or also a function of the charge profile of an automatic charger.
Cheers, T i m
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I'd be tempted to monitor the charge current and see what it is. Normally on a well designed charger its very low when fully charged, if that one is still charging high then it might well be that exception that has dodgyness in all cells. Brian
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On Friday, 17 November 2017 17:18:30 UTC, newshound wrote:

ponies with strange taste? Water is normally lost during charging rather than any other time, but 50ml a charge is a huge amount.
NT
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On 17/11/2017 18:11, snipped-for-privacy@gmail.com wrote:

Yes I know. That's why I am mystified. I've been looking after lead acid batteries for over fifty years, and have never had one behave like this before.
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On 17/11/2017 18:19, newshound wrote:

50g is 2.8 moles of water.
You would need 5.6 moles of electrons, so 540,000C
5 Amps would imply a gassing time of 10 days. So something strange is going on, unless you keep it connected to the charger for 10 days or more?
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On 17/11/2017 18:39, Fredxxx wrote:

To reply to the two posts together, I recharge the batteries with a traditional transformer/rectifier type car battery charger, so that the current drops off as it becomes charged (because the cell voltage rises). Once a cell becomes fully charged, the current it is passing causes electrolysis, so it "fizzes". In old batteries, the capacity may vary from cell to cell, so you may find one cell fizzing while another is not, that's a good reason to keep charging until they all fizz, but of course you do not want to concentrate the electrolyte by doing this for too long.
I realise that a charged battery may still have some trapped hydrogen and oxygen on the plates. So once it is charged, I will jiggle it and leave it open for a day or two in the hope that the gas all escapes. After that, I check the level and I don't normally find I need to add any more demin water.
IIRC this was originally an 80 amp-hour battery and it certainly still provides more than 10 AH at 12 volts, based on the lights that I run off it. And it is usually powering a couple of PIR lights that also get triggered through the night by cats, foxes, etc, so I suspect it's doing better than that.
I'm certainly not charging it for ten days. Might leave it connected for two days, and while the charger starts at 8 amps or so it has dropped to an amp or so after a day.
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On Fri, 17 Nov 2017 19:24:05 +0000, newshound

Ok.

'As it becomes near to being fully charged ...' ;-)

I think that happens in all / new cells within the same battery but by varying amounts. We used to minimise this (for racing) buy buying batteries made from 'matched cells'.

And the last one 'to fizz' also needs to fizz for a while to minimise stratification.

I think the risk is more the water loss from the electrolyte in general and exposing the plates than any change in 'concentration (as that will be redressed when you top up with water again).

And the water. ;-( Are you sure the cell caps aren't the recombination type (designed to allow the cell to vent pressure but to reduce the water loss)?

Assuming the electrolyte is above or at least level with the tops of the plates, I think you are supposed to top up (after it's been fully charged)?

Ok (the C20Ah rate would be only tested at that rate etc). So, for your 'calibration' of the battery as being 10Ah I believe you would need 48W of 12V lamp and would need to time it down to 10.5V or (ideally) higher (if not a deep cycle battery). So, for it to be 10Ah you would be able to run your (48W) lamp for 2 hours or a 100W for something less than 1hr?

Ok.

That sounds pretty reasonable for a largish / old LA battery. ;-)
So, I might be tempted to not remove the cell plugs when (or after) charging and see if that makes any difference to your electrolyte loss.
Cheers, T i m
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On 17/11/2017 20:09, T i m wrote:

Well also, you don't really want parts of the plates to "dry up".

Don't know. I used to work with a battery expert who knew all about this stuff, because there are BIG backup batteries on both nuclear and conventional power stations, but he retired to the wilds of Alberta. Certainly those cells are recombination type, but I don't know about ordinary car/tractor batteries.

What I am saying is that before charging, I top up so that the water is at the level of the marker above the plates, after charging the plates are almost always still covered, so I don't normally feel the need to add water then.

As an example, on the night of the big local firework display I got two hours of light out of about 50 watts of CFL, and I'd estimate that I have also had a similar amount of light out of the rest of the last charge.

Because you think they might be recombination type? But I am not really losing water during charging. It is vanishing when the battery is in service, with the caps on.

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On Fri, 17 Nov 2017 21:59:14 +0000, newshound

Quite, but assuming you keep the cell caps on and top the cells up after charging and check for any loss in between that might allow the plates to become exposed, you should be ok?

'Ordinary of what age / spec. I think most recent wet LA batteries (especially those marked as sealed but are still 'wet') I would think they would (have to) be.

Understood. However, I think more electrolyte appears *after* charging and so it could overfill the cell if you do it before.

No, quite and that would be expected. The 'issue' is that you should check the electrolyte levels more regularly so that they are above the plates at all times, not just as you are about to recharge them? ;-(
"If low on electrolyte, immediately fill the battery with distilled or de-ionized water. Tap water may be acceptable in some regions. Do not fill to the correct level before charging as this could cause an overflow during charging. Always top up to the desired level after charging."
http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

Is that 50W 'equivalent of incandescent' (and so say 10W of electrical load) or 50W of actual load?

Yes but of any type really.

Yes, I understand that and agree it doesn't make much sense. ;-(
If you buy a 'traditional' dry-charged LA wet motorcycle battery with a electrolyte pack, after applying the electrolyte and allowing some time (a few hours) for the plates to absorb it all, you fit the sealed plugs and attach the external vent pipe. From then on the only time you remove the plugs is if you need to top the cell(s) up with distilled water.
If I then leave a bike unattended for a long period of time ('years') I too would expect to see some plates exposed and find the battery ruined (sulphated). The most likely reason therefore is evaporation?
Cheers, T i m
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On 17/11/2017 22:33, T i m wrote:

I agree, modern "sealed" batteries are likely to be. IIRC this one was on a car about 15 years old (but it would have been replaced at least once).

Hadn't come across that point before, although I have seen small motorcycle batteries with a sort of overflow pipe. On a Japanese bike you are trying to get maximum capacity in minimum volume, so the plates are going to go near the top. But on this battery which came from a diesel car but curiously is identical to the battery on my old tractor there's a good half an inch of space between the level marker and the bottom of the cap threads. I agree that you might expect some change of volume between discharged and fully charged but its not an effect I have ever noticed on car batteries.

Actual load. IIRC, four 11s and a 9, or something like that.

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On Sat, 18 Nov 2017 20:02:47 +0000, newshound

If they were truly sealed (as in not operable for refilling) they would have to be.

Is that like Triggers broom? ;-)
Hmm, the technology has been about for some time now but you might be able to tell if they are by looking at them. eg, If they are obviously a plain plastic cap then they aren't. ;-)
https://www.sunaxy.com/products/rolls-r-recombination-battery-cap

<snip> >> No, quite and that would be expected. The 'issue' is that you should

Shouldn't the same theory apply to any flooded lead acid battery whatever it was to be used on. ;-)

<snip> >>> As an example, on the night of the big local firework display I got two

Ok.
Cheers, T i m
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On Saturday, 18 November 2017 20:51:27 UTC, T i m wrote:

Recombination catalysts are very pricey, the chances of them being supplied in a car battery are near zero.
NT
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On Sat, 18 Nov 2017 13:03:26 -0800 (PST), snipped-for-privacy@gmail.com wrote:
<snip>

So, when did you last top up your car battery?
Cheers, T i m
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