How long to leave a battery on charge?

[EricMark]

With a smart charger and 5 out of 6 batteries I want to keep in good order it is a case of clip and charger and remove again one or two weeks latter. Using an energy monitor on supply to charger it is clear as the battery charges it auto turns off, however I have one odd one out, a 95 Ah battery fitted to a Kia Sorento which will to start with follow the normal charge pattern, 3.8 amp, 3 amp, 0.8 amp the 0.1 amp. And it will at 0.1 every so often return to 0.8 amp charge rate, this is same for most of my batteries, the smaller ones will switch completely off then return to 0.1 amp.

However as time goes by with the kia battery the time between the two charge rates gets shorter and shorter, first time it switches to 0.1 amp it stays at 0.1 amp for nearly 12 hours, a day latter going to 0.8 amp charge rate twice an hour, the time at 0.8 amp is shorter, but last time ended up swapping between the two rates 8 times an hour, at which point I took it off charge.

The charger drops charge rate once it hits 14.4 volt, and lifts it back up again at 12.8 volt, so it ends up being pulsed, no other battery does this, so can't decide if to leave pulsing and see if settles, or to take off charge? Battery age unknown but over 4 years old.

 

[EricMark]

Well it seems temperature related, on a warm day maybe 4 pulses an hour, over night with frost on car 8 pulses per hour, which explains why I did not notice this happening last summer. With three cars in house hold and with Pandemic mileage around 60 miles a month combined for all three, plus caravan batteries which have been brought home do to caravan not being used, means at all times there is at least one battery on charge.

The smart charger where one can leave the battery on charge for weeks has been essential as clearly lead acid batteries take time to charge, as to pros and cons of constant 13.4 volt or alternating between 12.8 and 14.4 volt not really sure.

I know the idea of raising to 14.4 is to equalise the cells, where holding at 13.4 volt some cells can be slightly over charges and some slightly under charged, so once a day a pulse to take battery up to 14.4 volts and then allowing to drop to 12.8 likely good, but 8 times an hour not so sure about.

 

[Mike Johnson]

A decent lead acid battery off the car should hold a decent charge for at least three months, the battery in a BMW 5 series has held its charge for the last six months without charging, proved by starting the car once a fortnight or so.

 

[EricMark]

The two year old 95 Ah AGM lead acid fitted to wife's Jaguar XE needs charging around every two months, the eight year old 95 Ah AGM lead acid removed from my wife's Jaguar XE when the starting problem was wrongly diagnosed will recharge in a very short time once every 4 months, the 75 Ah flooded lead acid removed from caravan needs a top up every two months, and the 6 month old flooded 45 amp hour lead acid in the Honda Jazz needs a top up every two months, the 12 AH AGM lead acid in the jump start kit seems to last 6 months without charge, and the 7 AH VRLA also seems to last 6 months without charge.

The Kia Sorento 95 AH flooded lead acid has started the car without problem having been left for 6 months, however looking at the charge patten when put on the smart charger it had clearly discharged.
If I look at the charge patten here for the Jaguar XE I can see 1.5 hours at approx 3 amp so it has taken approx 5 Ah so for a 95 Ah battery clearly not discharged, but that 0.8 amp charge rate went on for two days, so there was some slight sulphate formed on the plates, if the car was in normal use this would not be a problem, but it is not in normal use, and to take for a 24 hour run to recharge battery is clearly not an option.

As said most batteries do as expected, it is only the flooded Kia battery which shows this pulse charge. Likely best option would be to swap it for the 95 Ah AGM battery and use the Kia battery for caravan, but not sure if radio coded.

 

[Mike Johnson]

I put quick disconnect fittings on all my car batteries on + and - if they are to be left for any period I disconnect them, be interesting to see if this has worked for the ride on lawnmower, it has not been started for over a year. ?

 

[EricMark]

The caravan battery was left for over a year, by time I was allowed by English and Welsh rules to go and retrieve it there was not even one volt showing.

The Lidi smart charger needs 7.3 volt to work out battery is 12 volt, so put a 7 Ah VRLA in parallel with the 75 Ah flooded battery and powered the charger from an energy meter so I could monitor progress.

Started at 0.8 amp (charging donor battery) then 0.1 amp (also donor battery) then zero and it stayed at zero for around 10 days, set to under 12 Ah as did not want to damage donor battery, so maximum it can auto go to is 0.8 amp which it did for around 4 days, then dropped to 0.1 amp, testing battery it seems OK, but not as yet returned to caravan.

The 10 days of nothing I found interesting, as it points to taking 10 days to soften up the sulphur enough for it to start taking charge, so it seems reasonable to assume it will also take 10 days with a part sulphated battery, so I aim to leave batteries on charge for a fortnight each time charged, to remove sulphur from plates.

The worry is if there is a shorted cell, then the battery will be held at around 12.4 volt so any battery charger will go to maximum output it can auto select. With the Lidi that is 0.8 amp so no real problem, with the Ctek it is the full 3.8 amp, and my caravan charger would go to around 18 amp as it tries to float at 13.4 volt.

This happened with a 35 Ah AGM pair of batteries fitted to my mobility scooter, not only did the faulty battery fail, but it also cooked the good battery. And that with a 4 amp charger, 24 volt of course, the 12.4 volt may have discharged the donor battery but as long as donor battery is smaller than battery being charged unlikely to do any damage.

This is why I like the Lidi charger, 0.8 amp is unlikely to produce enough hydrogen to cause an explosion and not enough bad egg smell to cause to much of a problem, but it does mean 100 hours to fully charge a 75 Ah battery.

 

[DPG]

The caravan battery was left for over a year, by time I was allowed by English and Welsh rules to go and retrieve it there was not even one volt showing.

The Lidi smart charger needs 7.3 volt to work out battery is 12 volt, so put a 7 Ah VRLA in parallel with the 75 Ah flooded battery and powered the charger from an energy meter so I could monitor progress.

Started at 0.8 amp (charging donor battery) then 0.1 amp (also donor battery) then zero and it stayed at zero for around 10 days, set to under 12 Ah as did not want to damage donor battery, so maximum it can auto go to is 0.8 amp which it did for around 4 days, then dropped to 0.1 amp, testing battery it seems OK, but not as yet returned to caravan.

The 10 days of nothing I found interesting, as it points to taking 10 days to soften up the sulphur enough for it to start taking charge, so it seems reasonable to assume it will also take 10 days with a part sulphated battery, so I aim to leave batteries on charge for a fortnight each time charged, to remove sulphur from plates.

The worry is if there is a shorted cell, then the battery will be held at around 12.4 volt so any battery charger will go to maximum output it can auto select. With the Lidi that is 0.8 amp so no real problem, with the Ctek it is the full 3.8 amp, and my caravan charger would go to around 18 amp as it tries to float at 13.4 volt.

This happened with a 35 Ah AGM pair of batteries fitted to my mobility scooter, not only did the faulty battery fail, but it also cooked the good battery. And that with a 4 amp charger, 24 volt of course, the 12.4 volt may have discharged the donor battery but as long as donor battery is smaller than battery being charged unlikely to do any damage.

This is why I like the Lidi charger, 0.8 amp is unlikely to produce enough hydrogen to cause an explosion and not enough bad egg smell to cause to much of a problem, but it does mean 100 hours to fully charge a 75 Ah battery.

If the overall battery voltage dropped to 1V then it will undoubtedly be permanently damaged. Even a deep discharge type battery would probably struggle to cope with this.

I'd either do what Mike says and disconnect it if it was going to be left for months, or connect a conditioner up.

 

[EricMark]

If the overall battery voltage dropped to 1V then it will undoubtedly be permanently damaged. Even a deep discharge type battery would probably struggle to cope with this.

I'd either do what Mike says and disconnect it if it was going to be left for months, or connect a conditioner up.

In the past I would have agreed, I have done all sorts, new acid, chemical, left on charge, and all seemed to fail, however I was looking for a cure within a short time, until I had a smart charger which would not charge over 0.8 amp I would not have left a old type charger on any battery for an extended time, too easy to end up baking a battery.

The first battery I tried for an extended time was a 7 Ah VRLA from a stair lift, the lift had been unplugged, the batteries went flat, and there was no manual wind on the lift, so only way to get it back to charging station was new batteries, and after getting it up and running I forgot the old batteries, some 4 months latter when father-in-law had died we found the old pair of batteries.

I did a rather dangerous thing, I put in parallel with a 75 Ah battery, and the Lidi charger, and forgot about it, and was rather surprised it recovered, so I put the two 7 Ah in parallel and this time on an energy meter, and it was as if some one had flicked a switch sat for 10 days nothing, then charged.

Well I had a few other batteries the same, some failed and some recovered, one that recovered was the jump start unit. But if not recovered after 14 days they never did recover, even if left for a month, but the surprise was how it recovered, not the slightest sign of life, after 6 days no change, then as said as if some one had flicked a switch.

As an auto electrician I had never had the time to leave a battery on charge for 14 days, if nothing after a day it went in the scrap. It was only after I retired I had the time and more to point a device which could monitor power used for a month or so which I could bring up on the PC and see what was going on.

 

[DPG]

In the past I would have agreed, I have done all sorts, new acid, chemical, left on charge, and all seemed to fail, however I was looking for a cure within a short time, until I had a smart charger which would not charge over 0.8 amp I would not have left a old type charger on any battery for an extended time, too easy to end up baking a battery.

The first battery I tried for an extended time was a 7 Ah VRLA from a stair lift, the lift had been unplugged, the batteries went flat, and there was no manual wind on the lift, so only way to get it back to charging station was new batteries, and after getting it up and running I forgot the old batteries, some 4 months latter when father-in-law had died we found the old pair of batteries.

I did a rather dangerous thing, I put in parallel with a 75 Ah battery, and the Lidi charger, and forgot about it, and was rather surprised it recovered, so I put the two 7 Ah in parallel and this time on an energy meter, and it was as if some one had flicked a switch sat for 10 days nothing, then charged.

Well I had a few other batteries the same, some failed and some recovered, one that recovered was the jump start unit. But if not recovered after 14 days they never did recover, even if left for a month, but the surprise was how it recovered, not the slightest sign of life, after 6 days no change, then as said as if some one had flicked a switch.

As an auto electrician I had never had the time to leave a battery on charge for 14 days, if nothing after a day it went in the scrap. It was only after I retired I had the time and more to point a device which could monitor power used for a month or so which I could bring up on the PC and see what was going on.

If you've got time on your hands then yes it maybe a worthwhile exercise. It is something I've played around with many years ago, but not as in depth as you I suspect.

To me it comes down one thing: will you trust the battery to do what it needs to so? If you need to rely on it to start a car for example.

 

[Strima]

Could well be a failing cell or even a manufacturing defect causing this, one cell might be dragging the rest of them down a bit.