Evaluating used gel-cell batteries?

Gell-cell batteries in UPS's: other than loading with a known load and timing how long it takes to drain the battery, is there a simple way to measure the
health of a gel-cell? Impedance?
Thanks, S.
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I will be interested to read the direct answer to your question.
A slightly different observation is that peeking inside the cells after removing plastic cover plate and the individual caps [taking precautions for acid spills] has often revealed very healthy looking plates that have simply dried out. In that case, I have injected 10 cc's or so of deionized or distilled water and recharged with an automobile charger. The SLA cells have then delivered many months of good service in UPS useage. Little luck reviving the cells when inspection shows significant "bloom" spanning the plates.

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On Wed, 8 Jul 2009 18:50:11 -0700, John Keiser wrote

How? I presume you drilled?
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SparkyGuy wrote:

No. Testing tells all.
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SparkyGuy wrote:

If they're 12V, charge them up and connect an automotive headlamp. You can calculate the AH capacity by how long it takes them to discharge to a certain voltage, you'd have to look up at what voltage a lead-acid battery is considered "dead" and be careful not to let it go much below that. From the voltage it drops to right after you connect the load you can calculate the battery impedance.
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wrote:

1. Charge the battery with the UPS or whatever. Attach a 12V tail lamp. Time how long it takes before the bulb goes dim. Compare with a known good battery. Not every analytical, but good enough.
2. <http://www.westmountainradio.com/CBA_ham.htm I have one of these and use it to characterize cell phone LiPo batteries and some gel cells. The method is the same a before. Charge the battery as best you can. Use the CBA II to discharge the battery. However, this time, you get a nifty discharge graph. As before, compare with a known good battery.
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Very careful not to reverse charge a cell. Do not discarge further than 10V. If you are watching the voltage when the first cell becomes completely discharged you can see a quick voltage drop by 2V, continuing the discharge would ruin the battery.
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If you load at 20% of the Amp Hour rating until the voltage falls to 11.9v you will have a quick test that is meaningful for go-no go test comparison with a known good battery. Another is to note the ability of the battery to taper off to 0 amps when charging to 14.4 volts. If the battery keeps pulling current it will likely self-discharge. This is valid for duali purpose automotive, RV and marine batteries, but a real deep cycle will act differently and start boiling with high voltages.and keep drawing current so beware.
Very careful not to reverse charge a cell. Do not discarge further than 10V. If you are watching the voltage when the first cell becomes completely discharged you can see a quick voltage drop by 2V, continuing the discharge would ruin the battery.
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A good auto battery seller should have an electronic tester. These give all the parameters of the battery including actual amp/hour capacity.
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*I'm not being rude. You're just insignificant

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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SparkyGuy wrote:

How about ESR? Bob Parker's Blue ESR meter will give you some static clues as to the condition of batteries if compared to known good ones...
http://www.flippers.com/esrkthnt.html (near the bottom of the page)
John :-#)#
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If you put an ESR meter accross batteries you will blow the meter!!! ESR is to be measured with no active voltage!
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Jerry G. wrote:

Not in this case - the Bob Parker ESR design can handle up to around 45VDC (input cap is rated at 50V) safely, but I have an 18V MOV on mine to help protect against higher charges.
If you had looked at the link you would see the chart shows a few batteries with typical ESR values. I posted that years ago (a fellow in AU created it) hoping to get some interest in folks seeing if ESR would help show if batteries are failing and be able to monitor them as a result.
A simple circuit that would start beeping when the batteries reach a certain ESR = time to test!
John :-#)#
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One easy way to tell if the battery is any good is "how many years has it been in service ?"
Most gell cell batteries have a maximum life of 5 years, this actually varies from as low as 3 years to 5 years life. If it's at three year battery and the UPS is not preforming as it should be, replace the batteries. Also try to get the same brand of battery that's in there for replacement. There is alot of third party batteries out there that claim to be just as good as the big name brands, but there not. I like Panasonic and CSB brands, they are a little bit more pricey, but worth it.
For discharging, look for the AmpHour rating on the battery. If you put a load on the battery that draws about that much current, you at "1 C" which means that the battery should supply that current for 1 hour before it is discharged. For testing batteries, don't use more that that amount of current because the AH rating falls off above it, and use the 10 volt rule that a previous poster wrote is a good guide.
Shaun
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The best test is to fully charge the battery, and then put a known resistive load accross it. The ideal load should be 25% of the amp hour rating of the battery. Time how long it takes for the battery voltage to drop 10% below its nominal voltage rating. A battery rated at 12.5 Volt nominal would be considered discharged at 11.36 volts. Fully charged with no load it should be putting out at least 13.8 to 14.5 Volts.
For example, if a battery is rated at 12.5 Volts / 7.5 Amp hours, the test load should be rated to pull 1.87 Amps at 12.5 Volts. The resistance of the load should be 6.7 ohms. The power dissapation would be about 24 Watts. Therefore the resistor for the load should be rated at 6.7 ohms at 50 Watts. Always use double the calculated watts for the resistor rating to prevent the resistor from over heating.
There are commercialy made battery load testers that have high wattage ratings to fit the required battery test range, and they have adjustable load resistance. Most of these testers have a load test that can quickly measure the internal resistance of the battery under test. (The battery internal resistance test is sort of hard on the battery).
With the 6.7 ohm / 50 Watt resistor accross the battery, it should take 4 hours for the battery to reach the 11.36 Volt level. The recomended maximum charge current for a 7.5 Amp hour battery would normaly be 1.87 Amps, unless the battery is to be quick charged. This value is 25% of the rated Amp hours of the battery. For quick charging the manufacture spec must be considered. Normally to exend the life span of the battery most manufactures use 50% of the 4C factor. This is why the battery would take 8 hours to fully charge. After the battery is charged, the charger will go to the float mode. The float charge would be 1/10 of the 4C factor which should be 187 ma in this case. The 4C factor is the 1/4 Amp hour rating of the battery.
For testing purposes, you can use higher resistances. This can also give you an idea about the battery's condition, not as accurately. Batteries do not always behave exactly the same at different loads. Internal thermo factors, and the stability of its internal chemical reaction are factors to be considered. The older the battery the less stable its internal stability may be. At greater loads, a battery will more easily exibit any defects or deficiencies.
As for the gell cells that are used in UPS's, from our experience we found that they are best to be changed during their third year. We found that after three years, they no longer give optimum performance. This is because when inside the UPS unit, there is some heat, and they battery is constantly charged. At times the UPS batteries are surge loaded at times. When these UPS's work in the battery mode, they generaly pull more than the long term recomended amount of power from the battery. UPS's are emergency devices, and the manufactures try to make them as economic as possible. Their weak point is usually the batteries. We have a battery change schedule for our clients which is every 2.5 years. This way we normally do not see any battery failures.
Jerry G.
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