Sealed Lead Acid batteries

[Norleif Slettebø]

I have a couple of sealed Lead Acid batteries (12V Panasonic brand ripped
from a UPS) that I've had lying around for some time.
When I got my hands on the UPS, it was kinda working, but it reported acc
error after a while, so I decided to take it apart, and inside I found 11 x
12V Sealed Lead Acid batteries.
When I was measuring the voltage on the batteries, most of them showed aprox
12V but a few was just showing 6-10V so I figured these was not working.
I stuffed the batteries in a cardboard box and put them in a shelf
(living-room temperature and humidity).
Now, almost two years later I picked up a few of them for a project I was
planning, and found that the charge had dropped to almost nothing. I hooked
one of them up to my power suply to try to recharge it, and turned the knob
to about 13V. When measuring the charge-current, It was only a few
milli-amps, and when increasing the voltage to 15V the charge current rised
to just 20mA, wich I think is quite low for these batteries. They are rated
at 6.5Ah/20HR and it also says "Initial Current: Less than 2.6 amperes" wich
is much more than the current I can drive into them.
I have no idea how old these batteries are.

 

[Marvin Moss]

A discharged battery like this has water rather than sulfuric acid as an
electrolyte.
As such it appears to be essentially an open circuit and will not charge.
I have had some luck putting about 50 to 100 volts DC on the battery in
series with a 100 ohm resistor.
As the battery starts to take a charge, it will start drawing more current.
The resistor is used to limit the current as this happens, unless you have a
current limited power supply where you can set it to 1 amp or so.
Eventually, the battery will take a normal charge at normal rates.
You must be careful not to let the current get too high with this method or
it could blow the seals on the SLA battery.
This does not always work but it is the only way I know to start the
rejuvenation process.

 

[Norleif Slettebø]

Thanks alot Marvin.
Your information seems to be right on as in my case, the charging current
are constantly increasing and the battery that is doing best has climbed to
over 150mA with a charge voltage of 15V.
Maybe I'll try to kickstart some of the other batterie that doesn't are this
high.

Aprechiate the help.

 

[Norleif Slettebø]

And another question I forgot to ask when typing the first reply:

"Then what?"

When I have (hopefully) my batteries back in action. How should I maintain
them to keep them in good condition?

 

[Marvin Moss]

Well, in general, a 12 volt lead acid battery can be maintained
for a long time if the charge voltage is held at 13.5 to 13.6 volts.
Trickle chargers do not do this. They will keep a constant
current of an amp or two for larger batteries and a few dozen mils for
smaller batteries.
In the long run, they will ruin a battery.
There are several chips like the PB137 that are designed just for what I
have advised.
They will charge at a 2 amp rate till the voltage hits 13.5 and then will
hold at that voltage.
You can keep 13.5 on the battery indefinitely.
There is some variation depending on temperature.
At nominal temps, 13.5 is about right.
If you are in freezing temps or Death Valley temps, then the 13.5 must be
adjusted accordingly.
Look up the datasheet for the PB137 and you will get a little more educated



This will not work in the long run as they tend to overcharge the battery.

 

[Marvin Moss]

Well, the answer is yes and no.
There are differences now between each of the cells.
Over a period of time of charge-discharge cycles, they may tend to even up a
bit.
However, there may be some permanent changes internally
so you may never get all of the cells to be uniform to one another.
That is a universal problem with all types of batteries where multiple cells
are used in series.

 

[jakdedert]

Well, the answer is yes and no.
There are differences now between each of the cells.
Over a period of time of charge-discharge cycles, they may tend to even up a
bit.
However, there may be some permanent changes internally
so you may never get all of the cells to be uniform to one another.
That is a universal problem with all types of batteries where multiple cells
are used in series.

I was unaware that lead acid batteries could even 'be' rejuve'd. If such is
the case, however, it would seem that in a system with individual cells like
the OP describes, it would be better to treat each individual cell
separately. Once each cell was brought up to optimum--or rejected as
unrecoverable and replaced--then normal charging and use would be possible.

Make sense?

jak

 

[Marvin Moss]

Yes, it makes sense if you can get to the terminals
of the individual cells. But in most cases, you can only
get to the outside terminals for the entire battery and not
the internal terminals for each battery. This is why it is
difficult to do what you have suggested, although
your method would produce much better results.

 

[Marvin Moss]

OBTW, I was rejuving lead acid batteries that were
discharged and had water instead of sulfuric acid in
the cell electrolyte.
This does not apply to a battery that is badly sulfated.
That is an entirely different problem and
is very tough (if not impossible) to fix.

 

[Marvin Moss]

BTW if you go to

http://www.uspto.gov/patft/index.html

and look up these two patents:

6242886 and 6184650

you can learn all about the theory of reversing the sulfation process.

 

[gothika]

Yes, it makes sense if you can get to the terminals
of the individual cells. But in most cases, you can only
get to the outside terminals for the entire battery and not
the internal terminals for each battery. This is why it is
difficult to do what you have suggested, although
your method would produce much better results.

I use alot of sealed lead acid batteries myself. Usually get about3-4
years before they die, regardless of cycles.
I use mostly powersonic and US battery and some yausua.
If I'm not mistaken the powersonics use what they call microcell
technology to get more density out of lead acid.
I'd cut one open years ago and all that it had was one large sealed
block.
I'd think that it's make getting at the individual cells pretty much
impossible since each cell is so small.(No it didn't have small
individual cells in a poly cell cluster. When I cut the block open all
it had was one large lump of electrolyte paste with very small pockets
of clustered cells.)
My battery dealer had always told me it was near impossible to
de-sulfate this type of battery.
I have several "deads" around and think I might give this rejuve
method a try tho'.

 

[Marvin Moss]

There is some question about the failure mechanism.
In some cases, the acid destroys the internal holders.
But if they were made out of material insensitive to acid,
you might get a few more years but then the manufacturers
would sell fewer batteries that way.

OTOH, depending on the extent of the discharge rates and depth,
the lead material can also "wear out" so to speak.
Especially if you leave the battery in a discharged condition!
This is why you always want to keep the batteries
at full charge or use some type of "trickle charger".
The trickle charger should have an upper limit of 13.7 volts
and not be of a constant current type.