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Revive a stored UPS (SLA) battery

Discussion in 'Electronic Repair' started by Ryan Underwood, Aug 31, 2005.

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  1. Hi,
    I have two hardly-used UPS batteries that were stored two years ago after
    the UPS was destroyed in a storm. I've now installed them in a UPS (APC
    Smart 700) that had its own batteries succumb to leaking. Unfortunately,
    they only have about 5V on each battery (supposed to be 14V), and the UPS
    immediately powers off instead of coming on and charging them like usual.
    I'm presuming this means that it doesn't like the replacement batteries,
    and not that the UPS had some other defect associated with the leaked

    I was thinking of using an automotive 14V trickle charger to attempt to
    charge them to the point where the UPS would hopefully accept them back.
    Does anyone know if an automotive trickle current is within the normal
    range of charging current for a sealed lead acid battery? Is this a
    dangerous thing to attempt? I hate to dump another $75 on batteries when
    I hardly got any use out of these.
  2. Arfa Daily

    Arfa Daily Guest

    I'd prefer to see them recharged via via a regulated proper DC power source,
    such as a CB 13.8v homebase power unit, rather than a rough DC source like
    an automotive charger. Small sealed gel-acid batteries are a little more
    delicate than hulking great car batteries. They can be connected directly to
    the output of the power source, but I would recommend putting an ammeter
    and a 5.6 ohm 10 watt resistor in the line just to monitor what's going on,
    and just in case there's any internal shorts on any of the cells. A
    voltmeter across the battery terminals wouldn't hurt also. Keeping an eye on
    the charge curve, via the meters, will give you a good idea as to the
    condition of the batteries.

  3. Jim Adney

    Jim Adney Guest

    I would try the automotive trickle charger. As long as the charge rats
    is small (try 1% of the AH rating of the battery) then you should be
    okay. When you do this, the battery voltage should come up to 12V
    within 1/2 hour. If it does not, then the battery probably has several
    shorted cells and can't be fixed.

    If the battery comes up to 12V at the 1% charging rate, then just
    leave it charging at that rate until the voltage gets up to 14.1V.
    This may take a week or 2, depending on how badly sulfated it is.

    Once the battery voltage while charging a the 1% rate rises to 14.1V,
    you should be able to put the batteries in the UPS and proceed

    Note that none of this insures that these batteries will have a lot of
    capacity once charged. You should probably run a "test" power outage,
    just to find out whether they are going to be useful.

  4. Guest

    Actually, something in the region of 12.6 V, no load. If they sat for
    two years and only have 5 V no load, the probability is high that they
    are junk.
    I may be misunderstanding you, but in my experience with a few different
    APC UPSes, the UPS doesn't have to be turned on (delivering power to the
    outlets) to charge. As soon as you plug the cord into the wall, it
    should start charging. Monitor the voltage across the batteries while
    you plug the UPS in; it should rise noticeably if the UPS is attempting
    to charge them.
    This depends entirely on the charger. What is its rating, in amps?
    What is the amp-hour rating of the batteries? This is usually printed
    on the battery. Panasonic even helpfully prints basic charging
    information on their sealed lead-acid batteries. You might look for a
    data sheet on the batteries you have. If they are no-names, you can
    still get an idea: these batteries come in several standard-ish sizes,
    so if you can find a battery similar in physical size and electrical
    capacity to the one you have, you can use the data sheet for that
    battery to get some idea of the charging parameters.

    If you have no other information, you want to set it up so that the
    battery will take 8 hours or more to fully charge. For example, I have
    a 600 VA UPS that uses 2 12 V 7 Ah batteries. Using a 6 amp charger
    would probably be too much, because that would recharge the batteries in
    a little over an hour. I might chance using a 1 amp charger (7 hours to
    charge), but it would be better to use one smaller than that.
    Assuming your 700 VA UPS uses something like the 2 12 V 7 Ah batteries
    my 600 VA UPS uses, $75 is way too much. I can replace these batteries
    for $15 or so each. As another example, I have a rack-mount UPS that
    takes APC's RBC18 "battery cartridge". If I buy it from APC, I pay
    about $70. If I buy the individual batteries from Digi-Key or Mouser
    and swap the wiring harness over myself, I pay about $25. Now, if you're
    using your UPS to support the payroll server at your office, or an oxygen
    machine at home, you might be interested in paying the extra $50 to
    secure the right to sue APC if the batteries crap out. But for almost
    everything else, DIY is the way to go.

    Matt Roberds
  5. James Sweet

    James Sweet Guest

    Go ahead and try the charger, but they're very likely shot at this point.

    In the future, put SLA batteries on a trickle charger while they're stored
    rather than waiting for them to go flat and sulfate. I use a 12v wall wart
    type transformer with a #47 incandescent lamp in series.
  6. Yup, you're right. Thought they were 14V for some reason. Hard to believe the
    longevity is really that bad!
    Well, it 'chirps' and the light flickers, but then there is no other sign of
    Interesting. Across one cell, it drops from 5.4V to 2.8V, when initially
    plugged in, then after the UPS chirps and dies, it gradually rises again. Not
    sure what's going on here.
    I see. Thank you for the thoughtful reply.
    I went to and saw $40 for the replacement. But it looks like
    that is actually both batteries, so it's not as bad as I thought.
    Yup. In fact the existing batteries, both the ones that leaked, and the ones
    that seem to have failed prematurely, were from different aftermarket battery
    retailers on the net. That's what I have been doing is buying batteries and
    swapping over the harnesses.

    Is it at all possible to buy a long-lasting sealed lead acid battery, or is it
    going to be a crapshoot no matter who manufactures it?
  7. Jim Adney

    Jim Adney Guest

    That makes me think that the cells are in there backwards.

  8. Jim Adney

    Jim Adney Guest

    Yes, a small incandescent bulb makes a very good non-linear limiting
    resistor for charging batteries.

  9. The cells are in the packs backwards, or the packs are in the UPS backwards? I
    don't see how the packs could be backwards, they are hooked up exactly as the
    old ones came out. The +/- leads are too short to reach to the wrong
    respective terminals anyway.
  10. Guest

    In a UPS that's used constantly in an area that has few power outages (an
    average on the order of a few minutes a month or less), the batteries will
    last 3 to 5 years or so, and that's about all you will get.
    Here is what I have observed of the startup sequence of some different
    300-600 VA APC UPSes. This starts with the batteries connected, the UPS
    switch off, and the UPS otherwise not connected to anything.

    1. Plug UPS cord into wall. UPS may chirp briefly, but will remain off
    with no power to battery-backed outlets.

    2. UPS will start to charge the batteries. You can see this with a
    voltmeter across the batteries or an ammeter in series with the

    3. Operate the power switch. The UPS will beep and switch on the
    battery-backed outlets. After a few seconds, it will do a battery
    test. The "on battery" light will come on and you may be able to
    hear the transformer humming quietly. If the batteries are good,
    this will last for about 10 seconds. If the batteries are bad, it
    will last for a second or two, before switching back to line power.
    The battery-backed outlets are powered during this entire period.

    4. When the battery test is complete, the "on battery" light will go
    out and the transformer will stop humming. The UPS should be charging
    the batteries again. The battery-backed outlets should still be

    5. Operate the power switch again. The battery-backed outlets will be
    shut off, but the batteries should still charge.
    This _may_ be the self-test failing, then the UPS trying to charge the
    battery. It could also be a battery that is so bad that any load
    applied by the UPS causes the battery voltage to crater. When the UPS
    detects the low voltage, it unloads the battery, which allows the
    voltage to rise again.

    You might see what each battery does, separate from the UPS, with a load
    across it. Something like a 193 (0.5 amp) or 1156 (2 amp) automotive
    lamp would be a good load. I suspect that you'll see the same drop in
    voltage that you see with the batteries connected to the UPS.
    In my experience, Panasonic and Power-Sonic make decent SLA (gel-cell)
    batteries in the common "small" sizes - 6 V or 12 V, 2 Ah to 15 Ah or
    so. Most of the Panasonic gel-cells I have used have been made in
    Japan, and most of the Power-Sonic ones have been made in Mexico. I
    have never had good luck with any gel cell made in China.

    Once you buy a good battery, you have to treat it right. With something
    like a UPS, about all you can do is hope that the UPS designer gave you
    a good charger, and keep it on charge as much as you can. Batteries
    don't like to sit around but they really hate to sit around when
    discharged. If you're designing your own charger, READ the technical
    notes from the battery vendors first! (Power-Sonic has a fairly good
    application note about how to charge their batteries.)

    Matt Roberds
  11. James Sweet

    James Sweet Guest

    I've gotten close to 7 years out of the batteries that are currently in my
    UPS, but it's possible to kill a SLA battery in a day or two under the right
    conditions, only takes once of discharging it too deeply and it's shot.
  12. Jim Adney

    Jim Adney Guest

    The impression I got was that the charger was coming on and driving
    current the wrong way thru the batteries, but on second thought, maybe
    what you're seeing is just due to some load that the UPS is drawing
    from the batteries for a brief moment, until it decides that there's
    not enough voltage there for it to work.

    I'd take the batteries out of there and just try charging them very
    slowly on an ordinary trickle charger. A small 6 or 12V bulb in series
    will help limit the current, which is something you really want to do
    if you want the best odds of salvaging cells left standing for a long

  13. Mike

    Mike Guest

    Yes, longevity is reduced by storage *without regard for topping up
    charges* ...
    It's testing the batteries. And then saying "You are kidding!". A lot
    of APC units will play dead when confronted with shot batteries. No point
    powering up if there's no actual battery backup to rely on :)
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