Leisure battery losing charge

Hi

I have had a campervan on & off the road for 5-6 yrs, but mainly laid up. It has a split charging system. When off the road I disconnected the main battery, but not the leisure battery. I've now charged it fully and topped up the distilled water, but when disconnected, a voltmeter shows that the charge just drops by 0.01 volts every 3-5 seconds or so. I've not put it back in the vehicle to test the use, but am presuming it's just going to lose it's power and may as well buy a new one?

I'm confused though as leisure batteries are designed specifically to run dead flat and be recharged all continuously, no? Which is why I left it in the first place when not using the vehicle.

Any ideas?

Thx

Hi, welcome to the forum.

It's normal for a freshly-charged lead-acid battery to show a falling voltage immediately after charging - the question is, at what point does the voltage settle and remain more or less constant? That will vary somewhat from battery to battery but it would typically settle somewhere between 12.9 and 12.6 volts off-load. If it's quickly dropping below 12.6 volts then there's a problem - either it hasn't yet reached full charge or else it's no longer capable of holding a reasonable level of charge.

Deep cycle batteries can be routinely discharged to a greater depth of discharge than starter batteries, but they're still not intended to be fully discharged. Do you know if there was any load still connected to the leisure battery during the period when it was laid up?

Also, did you check the off-load voltage (i.e. the voltage when disconnected from circuit) prior to charging, and if so, what was it?

Hi, thx for replying.

Well actually, it's not reached full charge yet - only hooked it up yesterday, but when I took the vehicle for a drive, I tested it afterwards and it was then that I saw it dropping from about 7v. Think it was at about 4 - 5 before driving, ie. how it's been left. There was no load connected to it apart from a 4 socket cigarette lighter extension which had a LED on. When I just checked it was at 11.35 and dropped to 10.6 within 90 secs or so but definitely slowed down. I've just put it back on charge. Sounds like it may be OK then, I'll leave it to see if the charger indicates it's full then?

I agree with everything Selectron mentioned above. I'd like to add that all batteries have a "life" though and for a lead-acid chemistry, that lifespan is typically around 5 years whether it's maintenance free, sealed, gel-cell, AGM, etc.

To try to get more life out of the battery you could pick up a battery desulfator and use it periodically on the replacement battery to get the most life possible out of the battery. It might extend the usable battery life by a year or two.

-Rod

I'll leave it to see if the charger indicates it's full then?

Yes, just allow it some time to come up to full charge. If the charger is able to indicate when it's fully charged then it's likely a smart charger (monitors the voltage at the terminals and adjusts the charging current to an appropriate level), so just leave it hooked up and keep your fingers crossed that it is still able to accept a full charge.

During the periods when the van is laid up, you should unplug the cigarette lighter extension socket - the LED will draw about 20 milliamps (20mA or 0.02A), which isn't much current, but as the days and weeks pass by that's a significant and unnecessary drain on the battery. With no load connected, the battery will only discharge at its natural self-discharge rate, which is very low and so that will allow you to leave it unattended for longer periods.

You shouldn't ever allow the voltage to fall as low as 5 volts, so keep an eye on the voltage every couple of weeks, and give it an occasional top-up charge (and the main battery too). Opinions will vary on the voltage level at which you should hook it up to the charger, but I'd suggest you shouldn't allow it to fall below 12 volts, and if it was my battery I wouldn't want to see it dipping below about 12.3, so that's the point at which I'd be giving it a recharge. With no load connected, it should take a while before the battery's natural self-discharge causes it to reach that level, so it should only be an occasional chore.

Thx

You say "shouldn't allow it to fall below 12 volts, and if it was my battery I wouldn't want to see it dipping below about 12.3"...

...but surely it'll always be reduced to less than 12v as when used with engine off it'll sometimes be drained to maybe flat? Isn't that the idea of a 2nd batt on a split charge system? 12.3 must be near fully charged?

Yes indeed - I should probably have clarified that I was still referring to periods when the van is laid up.

When the van is in use, with the leisure battery receiving regular usage, it will be discharged to some extent probably on a daily basis but it will also be recharged very shortly thereafter, and provided it's only left in the discharged state for short periods then it will come to no harm, and problems with sulphation will be largely avoided.

If though the battery is discharged to some extent and left for extended periods without receiving a recharge, then sulphation and a permanent loss of capacity become inevitable, so it's advisable to minimise the period for which it's left in the discharged state.

Until fairly recently, there was little that could be done about sulphated batteries and so they would end up on the scrap heap. With the advent of battery de-sulphators though, sulphated batteries can be reclaimed to some extent, and as Rod said, they can apparently be used on healthy batteries to maximise their service life, although that's an aspect which I've never really looked into.

I've used a couple of desulfphators with reasonably good results from at least one of them. A co-worker of mine, a power supply engineer, brought them to my attention. At the time we were working with a local electric go cart business to help them understand why their run time was considerably shorter than advertised after only a few charge cycles. The PS engineer suggested they try out desulfators which they did and they were very impressed with the results. I purchased one "just because" and have saved the battery from my car that sits all winter. I got in it in early spring and got nothing. I found the battery was only 4.3 Volts, so low that my smart battery charger would not even attempt to charge the battery. I stuck the desulfator on the battery with the charger. The desulfator provided enough of a load that the charger now would attempt to charge it and eventually brought the battery back to a full charge. I then continuted to use the desulfator per the directions and 2 years later have not had a problem with that battery (but I also trickle charge it over the winter now).

-Rod

It's been on charge for 2 full days now and the water is bubbling away - it's reached 12.7v but the charger still says it's charging. However, I just flicked from standard to sealed and back again and it turned to 'charged and maintaining'. Why would that be?

The voltmeter indicates that the volts are dropping once I disconnect, but as you say this is ok, but if I switch the charger back on almost immediately, it goes back to 'charging'

Also, not sure if this is anything to worry about, but the wells where the water goes each have a piece of the resin of the battery casing itself dipping into the water. Is this just an indicator for the water level, as one seems to be melted away/missing and is not long enought to touch the water?

Thx

... also meant to add - there is actually an indicator on the top of the battery - apparently an all green window/indicator is fully charged, but be damned if I can see and green in it in normal light - if I use a torch I can see some green but it's subtle - looks dark/black to me which states it's not fully charged...?! It's an ABS Systems battery if that's any help?

I've switched it off now and it seems to have dropped from 12.7 to 10.4v and is staying at that. Is that about right?

Sorry to be the bearer of bad news, but if it's gassing freely at only 12.7 volts and then falling quickly to 10.4 volts when removed from the charger, then you've lost one of the cells and the battery is almost certainly scrap.

Your battery is made up of six cells in series, each having a nominal voltage of 2.1V, giving a battery voltage of 12.6V - I think one cell has gone short-circuit, so you now have a five-cell, 10.5V battery.

It's pointless to continue charging it, because it will just boil the five cells but won't do anything to clear the short on the sixth - I don't know of any way to recover that, so battery replacement is the only option.

Just for future reference, those projections which you mentioned which dip down into the electrolyte are indeed electrolyte level indicators. In the event that the electrolyte level is low, distilled water should be added until the lowest point of the indicator is just submerged, and that should be done after charging. In the event that the level is so low that one or more cells has exposed plates, then just enough distilled water should be added prior to charging to cover the plates, and then after charging it should be topped up to just cover the indicator. I wonder if the sixth one really did melt? Whatever happened to it, if you can see such a clear abnormality then chances are that that cell is the bad one.

Mmm, well the one with the shorter part that isn't touching the water was bubbling away, however there was one cell which had a low level so I added more water - that one wasn't hardly bubbling so presume it's that which is dead?

Yes, that sounds very reasonable - with five cells gassing freely and one which isn't, you've probably found the dead cell.

I lost a battery to a short-circuit cell one time a few years ago under similar circumstances - my own car was laid up for months on end while I was driving a company car, but I neglected the battery maintenance and when I finally got around to charging it, I ended up with a five-cell, 10.5V battery.

Will it just mean that I have 85% at max charge? Or does it not work like that? What would have caused the cell to die then being that it's not been used (or is that what's caused it)?

thx

Dean

Will it just mean that I have 85% at max charge? Or does it not work like that?

It doesn't really work like that. If you still had full voltage but with only 85% capacity then it would still be very much a usable battery, but that isn't what you have.

While it's true to say that you still have 85% of the nominal voltage, and the five good cells might well be at something close to 100% charge, as a 12V battery it's pretty much useless. Any loads which are voltage-sensitive either won't operate at all, or they might operate unpredictably, and while I can't think of an example right now, there would probably be a scenario where damage could be caused to an accessory/appliance which was expecting 12V but receiving considerably less. I wouldn't trust it to do any task more complex than lighting a 12V filament lamp, which it would do happily, albeit at reduced brightness. Also, you'd have to come up with an alternative means of charging it because the 12V charger will overcharge the five remaining cells by some considerable margin. For all practical purposes, it really is scrap.

I wouldn't like to say exactly what might have caused the short-circuit, beyond saying that it's been caused by sulphation as a result of being left for too long in a deeply discharged state. It's happened to you, happened to me, will have happened to countless others too, so I reckon Rod was very lucky indeed to pull his 4V battery back from the brink.

Mmm, Ok, thanks v much for all ur help - there 'was' a lot of crusty white/blue/green salty stuff on teh neg terminal - is that the sulpates u refer to?

No, the damaging sulphation occurs internally, at the plates which form each cell. Obviously, they're physically inaccessible so the only way to keep the sulphation in check is to either keep the battery in regular use whereby the charge is always replenished shortly after discharge, or else by periodic recharging or continuous float charging of a battery which is in storage. I prefer the latter option and nowadays I float charge my battery when the car is sitting idle, which it frequently does for weeks at a time.

Edit: of course we now have another means of keeping sulphation at bay, which is the de-sulphators. Even with a de-sulphator though, it would still make sense to treat the battery kindly by keeping it clean, topped-up, and well-charged.