Battery State of Charge

[zoidberg]

I must confess my eyes glaze over when it comes to the arcane finer points of 'battery state of charge'. Being me, with a Masters' Degree in Procrastination, I realised today I'd left several flooded-cell batteries in my shed undisturbed for several months. I waved a multimeter in their direction and found 3 showing 12.0V while 2 AGM things showed 4.75V and 5.0V

I suspect the latter two are kaput, so have set them aside for recycling. The others I'll attempt to recharge, then see if they'll hold a charge.

Any thoughts? Besides muffled laughter....?

 

[Alex_Blackwood]

I must confess my eyes glaze over when it comes to the arcane finer points of 'battery state of charge'. Being me, with a Masters' Degree in Procrastination, I realised today I'd left several flooded-cell batteries in my shed undisturbed for several months. I waved a multimeter in their direction and found 3 showing 12.0V while 2 AGM things showed 4.75V and 5.0V

I suspect the latter two are kaput, so have set them aside for recycling. The others I'll attempt to recharge, then see if they'll hold a charge.

Any thoughts? Besides muffled laughter....?

Try charging all of them. You just never know

 

[jamie N]

As above, you never know. I've 2 70Ah Halfords leisure batteries that are about 12/13 years old. They've been slightly neglected during their life, down to 11.8v at one time, then reclaimed and recharged and kept 'happy' since about 5 years ago. They're on my boat and working well as I write. I've always made sure that they've water enough, and they're charged by solar & PWM on the boat.
I don't feel that they're 'hanging by a thread' as they support a fridge 24/7, and the normal running of lights & stuff onboard, alongside a 3rd leisure battery, without worry, pretty much throughout the winter.

 

[rotrax]

I have a 2007 AGM Lifeline 110AH battery. It has been-and still is- used as a 12v power source in the workshop. Two years ago, returning after 4 months away it, without needing a charge, jump started my old 1900cc Fiat Doblo diesel. I have just measured the no load voltage, 12.6v. Last time it had a charge was January. When removed from the boat in 2018 and bought home it was neglected for a year and voltage dropped to just 6v. A boost charge bought it back, been good ever since, so dont despair of your AGM's.

 

[pandos]

I had some agms that were completely flat after being unused for 5 years.. they came back to life and worked away until they were 17 years old...

You may have to find an old "stupid" charger to get them going as the smart chargers sometimes will not work on what it thinks is a dud battery...

 

[zoidberg]

Aw, shucks! Looks like I'm in the resurrection business....

And I'd already allocated the 'spare' space. Ho-hum.

 

[Blue Seas]

I've got a range of Optimate chargers in my garage (3's, 4's and 10's etc) but in this case I would highly recommend the Optimate 3 (de-sulphating / recovery charger) - I have used it on dozens of flat (+/- 1volt) batteries and it only failed to recover one single battery which had a distorted case and would get hot anyway (internal fault).
I has genuinely saved me 10 times what it cost at least and, once you get used to it's ways you soon know where you stand.
4.5 / 5.0 volts should be no problem if no actual battery defects.
OptiMate 3 - OptiMate

 

[Daydream believer]

My AGM batteries have shown the reverse.
In November when I laid the boat up disconnected the redflash starter & the 2 domestic ones
The voltage on all three was 12.7V.
They had been fully charged in October but left connected & do have a parasitic drain which I have struggled to isolate.
Hence the decision to disconnect
Yesterday on a very hot day I checked the voltages. It varied - still disconnected- between 13.41 & 13.31
Where the extra volts have come from I have no idea. I used the same meter.

 

[Alex_Blackwood]

My AGM batteries have shown the reverse.
In November when I laid the boat up disconnected the redflash starter & the 2 domestic ones
The voltage on all three was 12.7V.
They had been fully charged in October but left connected & do have a parasitic drain which I have struggled to isolate.
Hence the decision to disconnect
Yesterday on a very hot day I checked the voltages. It varied - still disconnected- between 13.41 & 13.31
Where the extra volts have come from I have no idea. I used the same meter.

There lies the clue. What was the temp. in Nov

 

[zoidberg]

Yesterday on a very hot day I checked the voltages. It varied - still disconnected- between 13.41 & 13.31
Where the extra volts have come from I have no idea. I used the same meter.

That raises a question about the Third Law of Thermodynamics.

Or Specsavers....

 

[Goldie]

I suspect the latter two are kaput, so have set them aside for recycling.

I renewed my 10 year old domestic battery bank this winter. At the suggestion of a friend, I took my 5 old batteries to the local scrapyard and came away £60 richer. No wonder marinas offer to dispose of them for nothing!

 

[sarabande]

Re the use of simple battery charger on a flat battery.

You may be able to revive the AGMs with a specific desulfation routine from a smart charger as suggested above, but it's worth trying a small, say 10W nominal, solar panel connected dreckly to the batteries in turn and leaving for several days with the panel facing S. The panel will charge at v low V around breakfast, and peak at c.15v at lunch. There's a 10% 'rule' from Vyv Cox about sizing.

This revived some old Optimas I had lurking in the shed, and they provided useful DC lighting to a LED circuit in the shed for at least a couple of years thereafter. I did not rely on the AGMs for anything mission critical or heavy duty e.g jump starting.

 

[zoidberg]

Thanks, all, for input.
I've run 3 of them though a 12hr re-charge routine using a smart charger - recommended by Sarabande - and they're each showing 12.75 or better.
Another one is 'in process'.
I'll test each for V again once they've settled, and may try to rig up a 'stress test' if I can work out how.

 

[PaulRainbow]

Thanks, all, for input.
I've run 3 of them though a 12hr re-charge routine using a smart charger - recommended by Sarabande - and they're each showing 12.75 or better.
Another one is 'in process'.
I'll test each for V again once they've settled, and may try to rig up a 'stress test' if I can work out how.

A better test is a load test such that you would use them in real life. Connect each battery in turn to a headlamp bulb or two and time it to see how long it takes to bring them down to about 50% SOC. Multiply the hours by the current draw in amps and you have your usable Ah.