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From: John Doe on 28 May 2010 14:37
Robert Roland <fake ddress.no> wrote:

> John Doe <jdoe(a)usenetlove.invalid> wrote:

>> does it degrade an SLA battery to rest it in any state but
>> fully charged?
>
> All lead-acid batteries degrade with time. The degradation rate
> goes up with increasing temperature and/or decreasing charge
> state.

Is the degradation versus charge state rate linear? I guess not.

> In other words: Keep them cool and fully charged.

Does the act of charging an SLA battery also degrade it? I have
always thought that charging a battery degrades it, but maybe that
is a misinterpretation of the maximum number of charge cycles.

Anyway... Keeping it fully charged is impossible here since it has
to be used. But of course degradation takes place over time, so I
guess that is why they emphasize recharging the thing immediately
after using it. And the deeper the discharge, the more important
that is.

Thanks.
--



















> Note that proper charge voltage is dependent on temperature, so
> if you keep the battery in the freezer, your charger must be
> able to adjust the voltage accordingly.

From: Sjouke Burry on 28 May 2010 18:45
John Doe wrote:
> Robert Roland <fake ddress.no> wrote:
>
>> John Doe <jdoe(a)usenetlove.invalid> wrote:
>
>>> does it degrade an SLA battery to rest it in any state but
>>> fully charged?
>> All lead-acid batteries degrade with time. The degradation rate
>> goes up with increasing temperature and/or decreasing charge
>> state.
>
> Is the degradation versus charge state rate linear? I guess not.
>
>> In other words: Keep them cool and fully charged.
>
> Does the act of charging an SLA battery also degrade it? I have
> always thought that charging a battery degrades it, but maybe that
> is a misinterpretation of the maximum number of charge cycles.
>
> Anyway... Keeping it fully charged is impossible here since it has
> to be used. But of course degradation takes place over time, so I
> guess that is why they emphasize recharging the thing immediately
> after using it. And the deeper the discharge, the more important
> that is.
>
> Thanks.
Very long trickle charge will kill one. That sulfates the plates,
and is difficult to recover from.
Also leaving a small consumer on for the winter period is a great
killer.
Often someting like a radio, a voltmeter, a computer chip, etc.
Best to remove one cable from the battery, to make sure.
From: John Tserkezis on 28 May 2010 19:44
John Doe wrote:
> I would like to learn something about proper care of sealed lead
> acid (SLA) batteries. Is there any good authoritative science on
> how SLA batteries should be cared for? I am searching... I suppose
> battery makers/distributors would be one of the best sources of
> information about that?

The long and short of it:

Don't discharge the battery.
Don't overcharge the battery.


That kinda impedes on your actual use of the battery, so, a more useful
compromise would be:

Don't discharge the battery any deeper than you can help it, and charge
as soon as possible afterwards.

While charging, don't exceed the maximum charge rate for your battery.

Use a float charger, and ensure the maximum float voltage is not higher
than the maximum spec. This varies with temperature, so may be an issue
if the environment changes widely.




As an example, we used 100A/hr or so SLAs in an application where they
were deep discharged (over a week or so) as a matter of course. Perhaps
left for a couple of days in that state, then charged afterwards.

We'd get end of life after about two years of constant abuse like this
- about 80% or less service capacity left before it was no longer
acceptable in our application.

Which is not bad, considering two years is considered the service life
of SLAs in more critical applications like UPSs and such, in an
environment SLAs must love.

> Specifically... I wonder why instructions that come with SLA
> batteries so strongly emphasize charging the battery immediately
> after use, without specifying how much use. Are they concerned
> that the battery might eventually self discharge too deeply? Or
> does it degrade an SLA battery to rest it in any state but fully
> charged?

Not quite, at deep discharge states, the plates under go irreversible
chemical reactions that prevent an ideal charge from taking place
afterwards.

There's more that can go wrong too. Which is why I said "don't
discharge the battery" not entirely tongue in cheek. :-)

From: Robert Baer on 29 May 2010 06:04
John Tserkezis wrote:
> John Doe wrote:
>> I would like to learn something about proper care of sealed lead
>> acid (SLA) batteries. Is there any good authoritative science on
>> how SLA batteries should be cared for? I am searching... I suppose
>> battery makers/distributors would be one of the best sources of
>> information about that?
>
> The long and short of it:
>
> Don't discharge the battery.
> Don't overcharge the battery.
>
>
> That kinda impedes on your actual use of the battery, so, a more useful
> compromise would be:
>
> Don't discharge the battery any deeper than you can help it, and charge
> as soon as possible afterwards.
>
> While charging, don't exceed the maximum charge rate for your battery.
>
> Use a float charger, and ensure the maximum float voltage is not higher
> than the maximum spec. This varies with temperature, so may be an issue
> if the environment changes widely.
>
>
>
>
> As an example, we used 100A/hr or so SLAs in an application where they
> were deep discharged (over a week or so) as a matter of course. Perhaps
> left for a couple of days in that state, then charged afterwards.
>
> We'd get end of life after about two years of constant abuse like this
> - about 80% or less service capacity left before it was no longer
> acceptable in our application.
>
> Which is not bad, considering two years is considered the service life
> of SLAs in more critical applications like UPSs and such, in an
> environment SLAs must love.
>
>> Specifically... I wonder why instructions that come with SLA
>> batteries so strongly emphasize charging the battery immediately
>> after use, without specifying how much use. Are they concerned
>> that the battery might eventually self discharge too deeply? Or
>> does it degrade an SLA battery to rest it in any state but fully
>> charged?
>
> Not quite, at deep discharge states, the plates under go irreversible
> chemical reactions that prevent an ideal charge from taking place
> afterwards.
>
> There's more that can go wrong too. Which is why I said "don't
> discharge the battery" not entirely tongue in cheek. :-)
>
As a "point" of reference, i have an old UPS by APC and replaced the
batery only once so far in the appx 15 years of "use".
Most of the time it just sits there - maybe on trickle charge, who knows.
But on rare occasion when the power goes out and i am online, it
keeps all running for a careful save and shutdown.
From: John Tserkezis on 29 May 2010 18:49
Robert Baer wrote:

> As a "point" of reference, i have an old UPS by APC and replaced the
> batery only once so far in the appx 15 years of "use".
> Most of the time it just sits there - maybe on trickle charge, who knows.
> But on rare occasion when the power goes out and i am online, it keeps
> all running for a careful save and shutdown.

:-)

Just because you *can* do that, doesn't mean you *should* do that.

The recommendation is two years, to ensure the battery doesn't
magically fail soon afterwards. In fact, in those conditions, they're
probably almost guaranteed to last double or more of that.

Problem is, "almost" doesn't cut it in a mission critical application,
thus the two year replacement recommendation.

This is why some UPSs have an automatic scheduled "test", where they
shut down the server but leave it powered on, go to battery backup,
ensure it lasts pre-determined amount of time and power up again.
Otherwise you have no way of knowing a battery has failed.

I should qualify my quoted constraints assume normal domestic SLAs.
Higher grade UPSs use higher grade batteries that can last many years
longer before the recommended replacement.
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