I just started with a new company and they have a stack of replacement batteries for UPS's located at the branch offices. The problem is, no one knows if these batteries are good or not, and the devices they go in are all scattered around different locations.

Is there any way to test an RBC using a voltage tester or anything like that?

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    How old are they? Lead acid batteries don't survive long when they don't have a trickle charger attached. – Zoredache Jul 10 '12 at 15:28
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  • unfortunately no one is sure just how old they are, and i don't see any sort of manufacturing date on them. thank you for the battery storage link though. – user50919 Jul 10 '12 at 16:00
  • There are storage battery testers that test batteries under load. I'm reasonably sure someone makes one for your size batteries, but don't know what sort of price it would be -- the first one I found was over $5000. – Daniel R Hicks Apr 20 '13 at 23:25

A simple $20 voltmeter will give a reasonably good indication, especially if the batteries have never been used. A lead acid battery should quiescently show 2.0 volts per cell. If the cells have failed, they readily show less than 1.0 volts per cell. For other battery technologies, other voltages apply.

Looking through my UPSs, it seems some use 12 volt batteries (6 cells in a case) and 24 volts (12 cells). The one which has been sitting unused for over a year is a 12 volt and shows 11.3 volts. That would indicate it is in fair condition, but certainly not new (I recall the charge controller had issues, not the battery).

A simple voltage test is far from conclusive. Rather it is equivalent to taking your temperature to see if you are sick. Temperature doesn't show all cases of sickness, but it is more than useful enough as first diagnostic.

For a more thorough battery test, a suitable battery load tester is useful. While inexpensive load testers are sold for car batteries, those use far too large a load for a UPS battery. Something in the 2 to 10 amp range would be more suitable, unless it is a mainframe-class UPS. You could MacGyver a small load, like a car headlamp in tandem with the voltmeter. Look at the battery voltage, enable the load. The voltage should drop a little, like 5% to 15%. A weak battery's voltage will plunge more than 30%.

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    It should be noted that the batteries must be charged before testing. – Daniel R Hicks Apr 21 '13 at 12:24

I first measure the voltage without load, if it's below 10.5 V for a 12V battery it usually means that a cell has reverted or shorted meaning that it is probably dead.

If the voltage is over 10.5 V i first charge is to full. Then i measure the voltage under load, say 10A for a 20 Ah battery, if it goes below 12.5 Volts I would consider in sulfated and use a desulphator for a period of time on it.

If it still passes i would consider it OK, and good if it does not go under 12.8 V under the same load conditions.

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  • Charge the batteries first. – Daniel R Hicks Apr 21 '13 at 12:24
  • Yes first charge, then wait 24 hours and then measure. – Gunnish Apr 21 '13 at 12:34

The only sure way to test the batteries is with a designated tester. These devices are not cheap. The meter injects high frequency ac current into the battery and measures the internal resistance. This reading is compared to a chart for standard sizes or to a known good battery reading. Google for industrial test equipment, battery tester, for more information.

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Go to ANY motorcycle shop and buy a battery tender and connect them up to your individual 12 volt batteries (remove all interconnects from the battery packs).

The Battery Tender will tell you when it's charging, or when it switches to "trickle" (green light comes on, or blinks green).

If it remains on CHARGE (red light, or on some types a yellow light) after 8 hours connection, the battery is bad.

Generally, on a multiple battery pack in a UPS, it only takes one battery to go south to have the whole bunch report as bad.

When you pull the pack out and connect the Battery Tender, lots of times it will charge for a very short while (often minutes, if not seconds) before the green light comes on. If that happens, good battery. Go to the next one in the pack and do the same.

Remember: Only test one battery at a time.

Remove all connections from the battery terminals before connecting the alligator clips from the Battery Tender.

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Any auto or motorcycle battery charger will work (set it on a low amperage charging) and charge the battery for 8 hours or so. I don't trust the cheap circuitry they sometimes put in there to tell you if the battery is good. After a good charge time, check the voltage across the battery and if its anything less that 12.0 volts, the battery is just plain no good.

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