Lead acid battery mystery.

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

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.

Yes it is certainly shagged from an automotive viewpoint, but it gives me a month or so of "free" lighting at the stables. And of course unlike a UPS this isn't in any way a critical application, I normally have a spare ready to go.

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. ;-)

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

Ok.

Cheers, T i m

Recombination catalysts are very pricey, the chances of them being supplied in a car battery are near zero.

NT

So, when did you last top up your car battery?

Cheers, T i m

That has been my point in this thread. You don't expect a good battery to gas when charged by a well suitably controlled charger.

Batteries can go without topping up for years. Hence the OP's experience is out of kilter with mine.

I can assure you it isn't due to recombination catalysts.

I'm not sure that is true. I've just bought 3 traction / cyclic spec 'gel' batteries (not wet / flooded) that are VRLA and gas whilst being charged during the balance phase (you can hear them doing so quite clearly).

It is good that stationary flooded cells gas to some degree when in the last phase of their charge to prevent electrolyte (and therefore charge) 'stratification' as the rising bubbles help mix the electrolyte.

I agree. My EV didn't have recombination cell caps and so did require regular distilled water adding and when left unattended for a long time, most of the cells dried out to some degree. ;-(

Cells do gas not only when charged but when being discharged and that includes when they are self-discharging. If the OP's battery is only

Cheers, T i m

Complex charge regimes usually have an equalisation charge phase where the intention is to 'overcharge' the battery so it gasses, hopefully undoing some of the sulfation and mixing the electrolyte. It's done as a separate process to absorption and float charging.

Given the quantities of water the OP says the battery has been consuming, even a complete self-discharge wouldn't cause 50ml to disappear from each cell.

As do the most basic transformer based chargers.

That would be a big *hope* IMHO.

Yes, that is a positive side effect of 'overcharge' gassing.

Yes, if you break down the phases logically with say a 'Smart' charger but still happens with a basic charger (to varying degrees, depending on the terminal battery voltage and the charge / current and voltage etc), during the end of the absorption phase (the last 10% of the charge).

I agree. The 8 x Crompton 6V x 200Ah traction monoblocks I was running in the EV would take that (each) and more if I left the checks for a bit too long (weeks rather than days) but I'm not sure even they would lose that (each) when the car was not being used. However, when left for a couple of years unused, even these large and fairly new (compared to the OP's battery) batteries lost enough electrolyte to expose the plates. If I checked them again now, all the cells are probably bone dry. ;-(

Now, that is either from evaporation or the plastic battery cases being gas-permeable to some degree (as is much plastic) and it's (the water) simply leaving as gas (H2O)?

Cheers, T i m

APC "Smart" UPS's do cook their batteries. I only have a little one (750 VA) and it used to kill a pair of 12 V 7 AHr SLA's in 3 to 4 years.

The last failure was of the "What's that funny smell?" "Seems to be under the desk" "Ouch the UPS is rather hot":

I then reduced the charge voltage and fitted a fan. UPS now reports around 30C internal temperature instead of the 40 odd before. This was in Mar 2014, We've had a few short mains glitches recently that the UPS covered, previously that sort of thing would have alerted me to kanckered batteries. Guess I need to give it a real test though, may be later.

My posh tester tells me a lead acid needs to be replaced when the nominal capacity drops by more than 20%. ;-)

Voltage is everything in charging a Lead Acid battery. Also, the higher the temperature the lower the ideal float charge voltage.

Anything more than 13.8V continuously applied is going to shorten the life of the battery.

They can but not always. I can't help feeling they would help themselves if they ran the fan at low speed to increase airflow, even when there wasn't a mains problem.

A couple of years ago I posted a very similar photo of a Yuasa Y7 battery bulging after being used in an APC UPS

However the Y7 range are designed as alarm panel batteries, they produce NP7 batteries for UPS type applications.

I found the "secret" commands to adjust the float voltage (perhaps with hints from you or someone else here) and set out to adjust mine, only to find they were already bang-on.

As noted above, mine has a fan, but only uses it when it's covering a mains problem. Quite annoyingly it runs it for the daily spikes of a couple of seconds around midnight when "something" at the substation adjusts for over-voltage.

Some ought to tell APC. I dug out the datasheet for the batteries, the charge voltage was way above what it should be for the temperature of the batteries, for bulk rate let alone float!

Not that APC UPS chargers have bulk and float rates...

And that might well be a reasonably criterion for an automotive battery, especially measuring at normal temperatures since the performance drops with temperature.

But this one is still doing its job, although it looks as though one cell might now be shorted, since this one isn't gassing. Didn't have a DVM to hand but will check the voltage tomorrow.

JOOI, What did you reset the charging voltage to on that APC SmartUPS? Presumably it would have originally been set to 27.6v. Did you throttle it all the way back to 27.0v?

BTW, I've never seen APC batteries so badly cooked as that. More typically ime, they may swell slightly in the beam, never developing a noticeable hump on the top. That battery pack is in an even worse state than the set of 3 NP7s that got cooked by my UPSonic600, an ancient pure sinwave inverter type - it has a Honeywell "PAT" sticker with test dates of December 1993 and 1994 stuck on the back panel!

None of my APC UPSes have been modern enough to be blessed by anything other than a dumb charging circuit (voltage regulated to 13.8v per 6 cell's worth of battery pack). Similarly for that monster Upsonic600 with its 3x12v7AH SLA 36v battery pack (a slide in tray, optionally filled with two bank's worth of battery packs) and an ancient Emerson 30 with a pair of 7AH SLAs.

I've long since retired the SmartUPS700 simply because of its unconscionably high maintenance consumption of 20W (virtually none of which goes into keeping the battery pack charged). I think I retired the venerable Upsonic600 just prior to that when it started to cook its second lot of batteries after just another 2 or 3 years of service.

The APC BackUPS500 that I bought brand new in the box at a radioham rally some 15 years back is on its second (single) NP7. I haven't tested that in anger since the initial half hour commissioning test of the 50 odd watts test load of my FreeNAS (now NAS4Free) box (left halted during the POST to avoid FS corruption if the test had exhausted the UPS battery before I could manually restore the mains supply). I've not really had a chance to safely put it to the test during the past 4 or 5 years, so it's anyone's guess as to the condition of the battery now.

I presume the battery is still be in good condition since the total power consumption looks to be just the normal 3 watts in excess of the base load of the NAS box. I keep a UK version of the Kill-A-Watt meter permanently in line to monitor total consumption of UPS plus NAS box just to keep an eye on this. The last time I finally got around to checking the UPS out to discover the battery had failed, I'd been observing total power consumption figures of 58 or more watts. The knackered UPS battery proved to be the cause of the mysterious rise in energy consumption, initially misattributed to the NAS box itself.

I suppose I aught to take the opportunity to properly test the battery and to update the boot image file and pull the now finally redundant 5yo

Anyway, it isn't only APC who use the 13.8v SLA float charging standard, it's pretty well every make of UPS. They don't care for extending the battery life unduly by choosing a less corrosive 13.5 v when the higher voltage offers the cheapest way to achieve the maximum autonomy from a new set of batteries.

The one or two year warranties typically exclude the battery pack since they treat it as a 'mere consumable' whose life depends on the number of outages it may have had to deal with during the woefully short warranty period. As long as the batteries can survive the initial one or two years without obvious signs of failure after handling maybe just one or two short lived outages, that's good enough for the manufacturers who are only too keen to supply replacement packs at premium prices every 3 to 5 years.

The modern UPSes might include improved SLA charge management algorithms these days, I just don't know whether any of the manufacturers are looking to gain a marketing advantage over the competition in regard of battery pack service life. One way to improve battery pack life would be to recharge to 13.8v then drop back to 13.5v with a monthly boost back to

I've kept a spare 12A SLA in good enough condition by solar panel charging alone for just a week or so per year to jump start my wife's Y reg 1.6 litre automatic Astra a year or two after buying the battery 2nd hand from a flea market stall some 5 or 6 years ago. It proved to be nearly flat when I got it home. Just 11.99v open circuit on my own DMMs as opposed to some 12.5v on a borrowed meter from another stall holder at the flea market - presumably, a meter with a low battery warning indicator I'd overlooked in my haste to get a reading before parting with my fiver.

I've checked it just now and I'm seeing a reading of 12.65v some 6 months after its summertime solar charging stint. A brief test with an H3

The fact that a charging regime of just once per year to 13.8v (peaking to 14.6v for short periods of an hour or so) has been enough to keep this battery in good condition, rather reinforces my theory that 13.5v is more than sufficient to keep the battery from sulphating at, presumably, some small reduction in effective usable capacity from a float charge state of

The choice of voltage level for continuous float charging of a LA battery is a compromise between a lower limit that defines an acceptable sulphation rate and an upper limit that defines an acceptable corrosion rate (along with water loss). I've no doubt that the float charge voltage also effects the maximum usable capacity as well so it's not too surprising that the maximum voltage is chosen to 'improve autonomy bragging rights' by the UPS manufacturers at the expense of a life shortened to a mere 2 or 3 years when it becomes the customer's problem (and their chance to sell premium priced battery packs - a win, win for the manufacturers - the inkjet manufacturers weren't the first to profit from the consumables market, just the first to do so so outrageously).