Need a rechargeable battery tester

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AntAltMike

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I have quite a few "Power Sonic" lead-acid batteries with varied life histories. I'd like to be able to test them to see if they still can hold a charge nearly as well as they originally did. I think some discharge quicker than others, but because they are used sporadically in test instruments that I turn on and off during jobs, I really have no reliable way of knowing whether they supported the instrument for ten minutes or two hours before needing recharging.

Last night, I drained and charged a couple of these batteries. I drained them by leaving the instrument they are powering on until the battery failed, and then left it on for some time after that, reducing their no-load outputs to 9-10 volts. Then I charged them for about four to five hours using the instrument's internal charger (a "dumb" charger), then I powered up the instrument again, recording the voltage level every maybe 15 minutes or so until it failed again.

I did that with two batteries. One supported the instrument for about two hours, which I think is normal. The other for about half an hour, which I think is unacceptably out-of-spec. I could continue with this test with other batteries and other loads, but the fact is, I can replace these batteries for about fifteen dollars each, so even if I ever develop an effective and reliable regimen for evaluating the health of these batteries, implementing it will cost me more than these batteries are worth.

What is available for testing the health of lead-acid batteries? I would think that, in addition to the battery's nominal output voltage level, there would have to be some provision for informing the test device of what the rated amp/hour capacity of the battery was.
 
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cdru

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It really depends on what your parameters are for testing as to how to test it. For instance, if you are only looking to light a light bulb, anywhere between 12V and just a couple may be sufficient to light the bulb. If you are powering something electronic, say like a computer, then you want as close to max as long as possible before it drops off to a predetermined level.

If you just want to test how long it holds a charge, hook up an analog clock to it. The power consumption for the clock usually is minimal, so it's impact on the test also is minimal. Plug in whatever you are using to drain the power as well as the clock. Record what time the clock starts at. When the power drains to the point where it won't power the clock, the clock will stop and you have an approximate run time.

My company use to do this as a basic test for battery backups. We'd plug a computer in along with a clock and when the UPS no longer could maintain the 120V, power was just shut off.


Are the batteries sealed? If not, measuring the specific gravity of the acid may also serve as an easy way to monitor them but won't tell you everything.
 
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AntAltMike

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I want to determine if the battery can sustain the load of the instrument it is installed in approximately as long as it could if it were new and had its original current sourcing capability or if not, then how much had it deteriorated. If it can only power the instrument for one fourth as long as it could when new, then I'll throw it out. If it can power it for one half as long or longer, then I'll probably keep it but occasionally retest it.

I was hopeful that there was some sort of consumer-grade, affordable meter that might be able to determine that by measuring a few parameters, like how much the voltage drops under near instantaneous loads, and how it responds to changes in charge voltage.

In another forum, someone directed me to a battery impedance meter which could be used to assess the capacity of a lead-acid battery, but it costs about $5,800.

When lead acid batteries get discharged below a certain level, they deteriorate in a hurry, and that happens a lot with older equipment which does not have an intelligent, low voltage shut-down circuit in it, so there must be a lot of people in situations like mine who lug around a meter with a rechargeable battery in it that we suspect we now are recharging more frequently than we used to but don't really know how much more often that we now have to recharge it than we would have to if we installed new batteries in it. I think I pay about $15 each for these batteries, plus shipping. If I could buy a tester for $100 or less that would tell me if they had significantly deteriorated, then it would probably be worth my while to buy one, but it surely isn't worth my time to set up unique draining and recharging regimens to determine that battery's health because it would be cheaper to just arbitrarily replace it.
 
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