Why do batteries seem to be dead and then come back to life if you let them rest?

[bigcol]

As above title

Just tested old batterys, that I took out, to be scrapped that were reading 12.2 4 days ago.

not been charged at all

Just tested them and all 12.6 and 12.8.?

 

Why?

 

Col

Edited May 27, 2015 by bigcol

[Keeping Up]

I'll bet that you put a small load on them for a short time the voltage will very quickly drop back down again.

[Nickhlx]

They were possibly on (a small) load ( or recently removed from that load, when you tested them first , and now they have had a chance to recover they are reading higher. Firstly, I would check with a known good multimeter ( or at least get confirmation of your readings from one or two other meters) and then re-test them, both "rested" and on a reasonable load of say C/10 or C/20 - say a headlamp bulb or two

 

Give them a full long charge at 14.4 volts ( wet lead-acid) until accepted current drops to one or two % of rated capacity ( i.e. 1 amp or so on a 100 aH battery) rest them for a few hours and repeat the tests.

 

If the batteries have been left in a discharged state for any length of time, they will be at least partially sulphated, although may be recoverable to some extent with repeated cycling between 40% and 100%.

If they are a few years old, it might be considered worthwhile to replace with a new set if the budget allows.

 

Hope that helps,

 

Nick

[bigcol]

Just checked again with a very cheap cigar type 12v gauge

And still showing charged?

 

Col

[bigcol]

If they are a few years old, it might be considered worthwhile to replace with a new set if the budget allows.

 

Hope that helps,

 

Nick

Thanks Nick

I have replaced them already last week for new as getting old. 2013/14 2 others were knackered and still knackered testing the same way maybe dragging the others down?

I left these 3 in the wheel house to take off and scrapped with the other 2

In total 7 batterys going to be scrapped

But these 3 still showing charge any way just put up for sale might be a good buy for someone

 

Col

Edited May 27, 2015 by bigcol

[bottle]

Colin

 

What they are showing is a voltage that intimates a SOC of approximately 100% but not their capacity.

 

Put a small load on them as mentioned before and they will soon drop that voltage reading and not be able to cope with the load for very long.

 

A bit like torch batteries, have you ever turned on a torch and it comes on bright but in seconds it goes dim, exactly the same phenomenon.

[Murflynn]

just put up for sale might be a good buy for someone

 

Col

................ and might be an issue for you under the trades description act unless you advertised them as scrap.

[bigcol]

................ and might be an issue for you under the trades description act unless you advertised them as scrap.

In total 7 batterys 2 of which are knackered

5 unsure

 

£60 the lot, scrapyard will give you that for scrap anyway

Just trying to do someone a turn

but will alter listing. Thankyou

Or maybe cart be bothered to help someone

Col

Edited May 27, 2015 by bigcol

[bizzard]

Warmth. Pop each one in the microwave for a couple of minutes for a big increase in charge or bung em into the fridge to kill em off once and for all. I heat torch batteries in the oven along with my dinner to save wasting gas, or on the fire to give them a bit more life, always did with the old Vidor and NEVER-READY's.

[bigcol]

Bizzard. I'm using and Your forgetting the electric eels

They working wonders

 

 

Col

[by'eck]

As above title

Just tested old batterys, that I took out, to be scrapped that were reading 12.2 4 days ago.

not been charged at all

Just tested them and all 12.6 and 12.8.?

 

Why?

 

Col

 

One reason that springs to mind is surface charge/discharge effect. All the battery chemistry takes place at the plates surface in contact with electrolyte, so the surface of plates can temporarily become depleted of charge after supplying a heavy load. Given time to rest, sometimes several hours, the chemical composition equalises throughout the plates thickness revealing previously hidden charge.

 

A similar effect can be observed when charging at high currents, with the battery taking extra charge after a rest.

 

Just measuring a high off load voltage does not neccessarily mean that there is an substantial capacity left though. It could plummit as soon as you try to take any power out, given that you thought they were US.