Battery care with cars not used much, discussion.

27 Jan 2008
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Llanfair Caereinion, Nr Welshpool
United Kingdom
OK I was back in the 80's an auto electrician, so not without some knowledge, but in the 80's it was easy, vehicle not being used, disconnect and remove battery, equalising charge every 2 months or so. I still do that with Christmas lights batteries used on the railway, smart charger moved battery to battery every week, so all batteries maintained ready for next year.

However modern car has things which need power all the time, door locks for example, so removing the battery is not really an option. And anyway when we want the car, we want it now, not in ¼ hour after I have refitted the battery.

Modern car also have battery charging controlled by engine management computer, so any battery charger needs to be controlled in a way not to upset the charging system, and also the valve regulated lead acid or absorbed glass mat lead acid (VRLA or AGM) have today replaced the old flooded lead acid with caps to allow water replacement.

So during lock down I had two 3.8 amp smart chargers which did the rounds car to car, keeping them ready to spring into action, however we have go use to living without going out much, and the cars still sit around unused for weeks, plus the odd time an interior light is left on, the latter resulted in charger coming out, but once the Jazz was re-charged moved charger to XE and realised battery at 11.9 volt, clearly far too low, I was brought up to think 12.4 was minimum voltage before re-charging required.

But it was pure luck, no failure to start, not text message on smart phone, maybe that system has not been paid for, but is there some better way to get informed when a car's battery is getting low? I noted before when XE was left on charge for a long time with smart charger at just before 12 mid day every day the charge rate would raise, clearly some thing in car activated at that time. The charger was plugged into an energy monitor so could see when charge rate changed on my PC.

But is there some thing which can send an alert to phone, or computer so when battery is getting low it reminds one to put it on charge. Be that due to not being used or a boot light stuck on, some alert.

If the battery on the XE is low, the stop/start stops working, so when being driven we are alerted when battery is low, but non of the cars, have any ammeter or voltmeter to show battery state. I remember the cig lighter voltmeters, but where the cig lighter is would not be able to read it, and the old volt meter was analogue and reading between 12.4 volt and 12.9 volt which I consider is the range expected for a charged battery in storage, is near impossible with the simple plug in devices.

The Sorento is really only for towing, so that can sit unused for months, I do try to use it from time to time, but my memory is not good at working out oh it's been 3 months since I used that car.
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There are all sorts of smartphone apps that will Bluetooth to a little dongle that you plug into your diagnostic socket and give you more data than you could ever want. I imagine system voltage would be one of the most basic bits of data floating round the system, but might be worth doing some research to make sure your exact model is supported by whichever device you choose. Unfortunately, if your car is parked out of Bluetooth range, it might not be the solution you're after, but it would work whilst driving.
As I have suggested before, my car spends lots of time in the garage unused and has a 20mA discharge. I have it on a dumb voltage limited charger, which is powered up for 20 minutes each day, via a Smart Plug to charge it. The charger plugs into the car via a special ciggy socket I put in for the purpose, almost directly across the battery, though fused. I wired a home made flashing LED circuit across the charger lead, which consumes maybe 1mA fixed to the ceiling, that jut confirms the charger lead is properly connected to charge at a glance.

The caravan battery I take care of manually, giving it a boost every couple of months.
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Thank you for replies, I am aware that charging too often is as bad as not enough, but no car is parked where I can really leave it connected to a charger 24/7, it would need some form of outside socket, which is of course possible.

@Harry Bloomfield is in real terms what the smart charger does, my cheap Lidi charger will charge until 14.4 volt then stop until volts drop to 12.8 volts, which with the Jaguar which has a newish AGM battery that means a 15 minute charge once a day, some thing in the Jag must activate same time every day.

Moving house I had other things on my mind, and the caravan battery went below 7.5 volts, so the smart charger sees it as a 6 volt battery, so I put a 7 Ah 12 volt battery in parallel also powered the smart charger through an energy monitor connected to the PC. The result was not what I expected.

It sat for nearly two weeks doing nothing, then as if some one had flicked a switch, it started to charge, the charger being used would only go to 0.8 amp unless manually reset, so first day was just 0.8 amp, then manual reset and 3 amp dropping to 0.8 amp then 0.1 amp and the battery behaved as if it had never been abused.

In the past I would have given up well before that point, or tried silly voltages, or put so extra acid in the cells, the idea it could recover after so long had not entered my mind.

But it did point out how long it takes, and to jump start and go for a good run is clearly not going to replenish the battery, unless good run is over a week.

In the past I have worked with plant which was only used once in a blue moon, but in the main they had Nickel Iron batteries not lead acid. Or were on 24/7 float charge.

So we have it seems a few ideas on battery care.
1) Float charge is not good as the cells can become unequal, @Harry Bloomfield idea and how the smart charger works is better.
2) AGM batteries can be left longer between charges than flooded.

But no one seems to say exactly how long between charges. Once every two months, once every month, once every six months, at the railway where I volunteer the Christmas lights are lit using lead acid batteries, we have around eight, and each time I go in, around once a week, the smart charger is moved to next battery in line, because often they are taken off charge while I am away, I use a volt meter and the battery with lowest volts is the next one to be charged, been volunteer three years now, and batteries have lasted even with the huge gap due to Colvid.

But a VRLA or AGM should last at least 10 years, even a flooded could last that long, so really looking at a 15 - 20 year life, when only used at Christmas, time will tell.

As a 6 year old, so around 1957, I found some gel lead acid batteries in my dads loft, topped up with distilled water put an charge, and they worked the old radio with a triode valve, since war surplus these batteries were at least 8 years old, and they were used until I was about 10 on and off, so long lasting lead acid nothing new.

At around 10 I got some more war surplus batteries this time flooded, they had been dry charged, so filled with acid and off they went, still using them when I left school, so well over 20 years old. OK should not call them batteries as single cells.

The car battery however was a different beast, it needed to deliver a high start current, but in the 80's Lucas marketed the battery for life, if fitted to same car owned by same person if the battery failed it was replaced free of charge. Clearly not any longer as Lucas part of British Leyland which has now gone.

But mothers mobility scooter bought around 2004 battery lasted until 2018 when a cell went short circuit so all other cells were fried. Narrow boat batteries seem to have a very short life, but likely due to being left discharged for too long, alarm batteries and stair lift batteries also seem to have a short life, likely to being over charged, measured mothers batteries on charge it was 32 volt, seems a bit high to me for a pair of 12 volt VRLA, and batteries lasted longer when being used every day to when sitting there weeks on end not being used.

Two to four years for alarm and stair lift batteries is rather a short time.

But this all means the experts seem not to know how to treat batteries, we should be seeing 10 years for stair lift and alarm batteries, the old milk float we expected 10 years, with the battery deep cycled every day. Same with fork lifts.

So it is not some thing one can just read a book and get answer, why did the war surplus battery last so long?