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Testing a UPS battery

L

Lugztaz

[H]ard|Gawd
Joined
Jun 21, 2004
Messages
1,783
I don't know a whole lot about electronics, but I have about 9 UPS that I got from my dads work. I will be keeping a few and he will be taking the rest to a different office.

We don't know how old these are, nor how much they can even hold anymore. I have a multimeter and I would like to test the batterys inside of them. They are easily removed by two screws and the two connectors so I have one out but I'm not sure how to test or what to look for.

Can anyone give me some hints?
 
When the battery is disconnected, it should measure 12.6V at no load if it's about fully charged, 12.2V means it's just 50% charged, and 12.0V is 25% charged -- just like a car battery. Because small differences in voltage mean big differences in state of charge, you should use a digital multimeter, preferrably one that displays at least 3 1/2 digits (2000 count or higher).

It's probably better to measure the battery voltage under slight load, roughly 5-10% of its amp-hour rating/hour because some batteries will measure OK at no load but drop at least 1V under any load. IOW if your battery is rated for 7 amp-hours, use a load of 0.35 - 0.70 amp. Resistance = volts/amps, or 17-34 ohms in this case. The resistor must also be able to handle the power, which is volts^2/ohms, or 144/17 watts or 144/34 watts. But the resistor should rated for at least 2-3 times the actual power so it doesn't get scorching hot and melt plastic or burn stuff (including skin).
 
Check the years stamped on the battery itself.
 
Which brand UPS? What voltage battery? Any other useful indications on its label?
 
How about the fact that on the first one I let charge over night, kill power to the UPS and try to boot a PC I get nothing? :)

Will get battery numbers here in a sec...
 
I think that test says a lot already, unless they disconnected the battery before you got it? ;)
 
I had taken the battery out and looked at it, so I know it's connected when I put it back in.

I just tested another UPS, killed power to the powerstrip and the UPS started screaming at me but the PC continued to run.

My digital multimeter is dead(battery) so i will have to do the testing later.
 
Ok on the second unit(testing both with the batteries pulled out) I was getting 13.33V and on the first one I got 3.??v so I can only assume it's dead as it was plugged in all night.
 
Yup, seems like that first battery is a goner. So it is a 12V battery? Let us know whether you can find a replacement for it.
 
Well hell, I was gona ask where to find replacements and if it's worth it or not :)
 
Well, what brand and model PSU is it? What are the specs on the battery and other relevant information?
 
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