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greybeard
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Joined: 04/01/2010
Location: Australia
Posts: 161

Posted: 03:30pm 21 Dec 2013

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I have a qty of 12v 7ah sla brick batteries. Some have been recycled from UPS use and other purchased new and of varying age from ~10 years to a year or so.
I use several of them when I go camping a couple of times a year and the rest of the time they site unloved in side a spare room in the house ( reasonably consistent temperature environment ). I put them individually onto a top up charge every 4-6 months and then just prior to use. With the expected use of these batteries they should be well dead of old age before any charge/discharge degradation occurs.
Question is apart from the entertainment value of connecting/disconnecting the charger individually to each of the batteries is there any merit in changing the treatment of these batteries in regard to maintaining there usefulness?
I'll start by saying that I am a sceptic in regard to desulphators until I can see some scientific evidence with side by side treatment of identical batteries rather than anything I've seen so far.
Would there be any benefit in connecting the batteries to a float charger until needed? ( as opposed to the random recharge done at the moment )
If connected to a float charger would it be acceptable to just connect them in parallel to the charger?
Basically I'm looking for minimal effort. If making up a parallel wiring loom and leaving them on float charge is going to improve ( or not be worse ) the shelf life of the batteries as opposed to random charge/self discharge then I'd go for it.

greybeard
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Joined: 04/01/2010
Location: Australia
Posts: 161

Posted: 11:08pm 21 Dec 2013

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I've been researching this most of the day and the consensus appears to be that charging the batteries in parallel is probably ok. But checking individual batteries periodically is a good idea to check for any dead cells.
Opinion seems to be divided regarding leaving SLA's on float or periodic charging. Some UPS's utilise a cycle of charge, boost, float, no charge and claim that this increases the battery life.
I might just make up some cable harnesses so I can charge multiple batteries in one go and leave them on float for an indeterminate period of time. Sort of what I've been doing but less plug/unplug.

Downwind

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Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 01:18am 22 Dec 2013

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What voltage do you call Float for a SLA.

Perhaps one option is to parallel some cells and use a power point timer to activate a charge cycle, at least that way you should not cook any bad cell.

Its best to fully charge each cell before adding them to a parallel string, any cell that dont come up in voltage to equal other cells should not be placed in the parallel string.

Pete.

Sometimes it just works

greybeard
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Joined: 04/01/2010
Location: Australia
Posts: 161

Posted: 03:52am 22 Dec 2013

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Cheers Pete.
The float voltage for SLA will probably be scientifically chosen to match up with whatever the charger I end up using is set to

but I'll research it a bit more as there seems to be some variation ( yes, I know that it does also vary with temperature ).
I like the idea of a power point timer, fits in well with my hands off approach.
rgds
Rod

Tinker

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Joined: 07/11/2007
Location: Australia
Posts: 1904

Posted: 04:08am 22 Dec 2013

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If this was my problem I would invest in a small solar panel (<5W) and place it somewhere so it gets sun only an hour or two a day. The panel would keep the batteries charged and if its a 30 cell panel you might get away without a regulator.

Klaus

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