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?
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?
<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?
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
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.
This newsgroup posting comes to you directly from...
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?
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.
'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
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
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?
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
Cheers, T i m
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.
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
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
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
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.
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. ;-)
<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
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