Looking after rarely used SLA batteries

[mtbandy]

Hi all,

I was just wondering something. I have all these large 86Ah 12v SLA batteries sitting here fully charged, and they have been like that for about 3 months now (not attached to a charger - just literally stood there!). Last time they were used was when I was away camping, and drained them all down to about 70%.

I've been chacking the terminal voltages fairly often, and even after 3 months they are all around 13-13.1 volts so I haven't done anything with them in 3 months.

I'm getting slightly uncomfortable that these things appear to be looking after themselves! So simple question really, would exercising them slightly (ie. hook them up to my small solar system so that they get very shallow daily cycling) do them any good? I've read that cycling them can 'help open up new reaction zones' or something along those lines.

Either way knowing my luck they will be shot by the next time I really need to use them properly, but anything to help slow that process down would be good.

I thought I had most of my battery theory nailed, but this is a sort of compromise that has me puzzled which way to go - how to look after rarely used batteries!

Cheers

[Flux]

The best thing is to float them at the voltage recommended by the makers if you have a suitable charger.

Failing that they do tend to hold their charge much better than wet cells and a refreshing charge may only be needed after perhaps 6 months, just keep watching the voltage and re charge as soon as it starts dropping.

Sadly you are right and they will eventually die whether you use them or not. The cheap ones may have a life of 5 years when not used, the best grade manage about 10 years. Many on standby duty are never used except for equipment tests and are thrown out after a certain time, whether they are still ok or not ( beyond a certain age nobody can be certain they will do the job).

Flux

[AbyssUnderground]

Your best bet would be to get a charger that you can set the voltage on, and float them at 13.2-13.4v to avoid the risk of them discharging. Failing that, a small solar panel in parallel with all of them should keep them topped up nicely. I'm not talking those 1.5w panels, in my experience they've been useless. I'm talking 5-10w if you can. Maybe a cheap charge controller as well. It all depends how much you're willing to spend to keep them in tip top condition.

As flux rightly said, you might just need a reconditioning charge every few months on your usual charger. If you're using one at the moment, why not use them all in parallel right now? You'd use each one and would only be shallow discharging compared to using the one you're using now. It would reduce the workload of that one battery.

[wooferhound]

I purchased a battery 4 years ago for RE use. I used it a couple of months and then moved. The battery sat unused and uncharged for 4 years. Then I installed my new Solar System 2 months ago and that same battery is working wonderfully and powering my DSL modem right now.

Here are some links with related information

http://www.fieldlines.com/story/2005/4/2/63834/21217

http://www.fieldlines.com/story/2007/7/10/03658/3597

[ruddycrazy]

Similar story here Woof,

                        Those 24 2 volt 275ah agm's I got sat for nearly 10 months with me only trickle charging them a few times and in a 24 volt array both banks sat on 25.6 volts even after a month or 2. I've since hooked them up in my shed and with using the 3kw inverter all day they still hold around 25 volts. Even my other bank which I got from the scrap yard 30 6 volt 110ah agms are holding up well after 2 years use in the shed. with both banks costing less than $700 it's cheap power for my shed and the 275ah ones are only 3 years old, the 6 volters are now 5 years old.

Cheers Bryan

                     

[mtbandy]

Thanks for the replies guys, I think I'll parallel them all up then and put them onto a little boost converter charger that I have (~12vdc to 13.8vdc). Sounds like it'll be better than just forgetting about them.

The reason I haven't connected them up to my existing solar system is mostly because my existing charge controller is fixed at 14.2 volts, and this seems to cause the cells to vent (recommended float of these standby batteries is only 13.65v). I'll eventually mod the controller to cut off at 14 volts, hook up all the batteries and start using more solar power!

Cheers

[AbyssUnderground]

My 90Ah SLA doesn't vent on 14.2v, so maybe you're just a bit paranoid? Remember floating is when its charged, and it being a solar system, it being charged is going to be rare.

[ruddycrazy]

Eh Mtbandy if your worried about that extra voltage just stick a diode in 0.7 volt drop too easy.