Sealed lead acid battery maintenance?

[John Doe]

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?

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?

Thanks.

 

[Phil Allison]

"John Doe"

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?

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?

** If an SLA battery is left in a discharged condition (ie less than 2 volts
per cell ) for a long enough, ie weeks or months, it will corrode internally
and be ruined. Same goes for most lead-acid car batteries too.

Not true for Ni-Cd or NiMh cells though.


...... Phil

 

[Robert Roland]

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.

In other words: Keep them cool and fully charged.

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.

 

[John Doe]

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.
--

 

[Sjouke Burry]

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


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.

 

[John Tserkezis]

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.

 

[John Tserkezis]

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.

 

[Martin Brown]

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

And it is at least worth the occasional visual inspection of the
batteries for obvious signs of swelling and distortion of the case.

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.

UK replacement is annual test and replace on fail or 5 years old
whichever happens sooner. Mine live in a fairly cool environment and
would still hold a decent charge when retired. I have seen some 8 year
old ex UPS cells that I took to the recycle centre in a bucket because I
was unsure if the plastic cases would hold out. They were very obviously
mangled shapes with big bulges but still not leaking.

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.

Exactly. No point in having an emergency back up that doesn't actually
work when you need it. Same applies to emergency lighting.

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.

Even so it makes sense to check them annually. You don't really want a
failed SLA spewing corrosive electrolyte over your UPS.

Regards,
Martin Brown

 

[John Tserkezis]

And it is at least worth the occasional visual inspection of the
batteries for obvious signs of swelling and distortion of the case.

Unfortunately, that's not an effective enough test. Most fail at end
of life looking like new. So a visual test alone is not enough.

Some of the large commercial scale units perform an internal battery
test with a limited load, with the marketing blurb claiming it's good
enough to detect a dud battery even while the unit is live and running,
never having to go offline for the test.

UK replacement is annual test and replace on fail or 5 years old
whichever happens sooner. Mine live in a fairly cool environment and
would still hold a decent charge when retired. I have seen some 8 year
old ex UPS cells that I took to the recycle centre in a bucket because I
was unsure if the plastic cases would hold out. They were very obviously
mangled shapes with big bulges but still not leaking.

We were so poor, we had to used other's disposed of batteries as our
new ones.

We went so far as trying to recover open circuit SLA cells. We dumped
10-15+ volts into the things (single 2v cells!), till they took a
charge, then they somehow magically worked. For a while anyway.

That's on good quality (albeit old) cells. I've never really had any
luck reviving cheapies.

Even so it makes sense to check them annually. You don't really want a
failed SLA spewing corrosive electrolyte over your UPS.

True. I've seen batteries go short, overheat, dry out and become
basically useless. A real chore to get the buggers out because they had
warped so much.

No-one noticed because the power had never gone out in that time (many
years) till someone thought it would be a good idea to actually look at
it...

 

[legg]

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?

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?

Thanks.

Check the Yuasa website for VRLA operation and maintenance
recommendations:

http://www.yuasabatteries.com/literature.php
http://www.yuasabatteries.com/pdfs/TechMan.pdf

There used to be some good stuff from Exide, but I've lost links to
the electronic format manuals.

RL

 

[legg]

See sci.electronics.repair - under the header
" Evaluating used gel-cell batteries?" for real longevity solution.
Charlie+

This server only provides ~ months back postings.

If it's archived somewhere, I'd be interested.

RL

 

[Jasen Betts]

This server only provides ~ months back postings.

If it's archived somewhere, I'd be interested.

dejanews (now called google groups)



--- news://freenews.netfront.net/ - complaints: [email protected] ---

 

[Cydrome Leader]

Unfortunately, that's not an effective enough test. Most fail at end
of life looking like new. So a visual test alone is not enough.

Some of the large commercial scale units perform an internal battery
test with a limited load, with the marketing blurb claiming it's good
enough to detect a dud battery even while the unit is live and running,
never having to go offline for the test.

I've chatted with and watched quite a few large (tens to hundreds of kVA)
UPS maintenance techs.

the standard procedure seems to be a visual check, retighten all
connectors, measure voltage across all batteries, then again with the UPS
in test mode where there is a real load across the batteries.

They can usually spot a bad battery before it would cause problems.

larger UPSes have redundant strings of batteries so even with a dud you
can still operate.