When using a uninterruptible power supply how long does it preserve the original capacity? Say I buy a UPS that holds the necessary load for 10 minutes - I don't want it to unexpectedly come into state when it dies 30 seconds after a blackout starts.

Hw many years does it usually take to exhaust the battery without its misuse and abuse? Are there any known examples?

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    Note that when a UPS suggests a battery needs replacing (such as the APC units do) it actually means that the battery has only a short time left before it fails (like a month). It doesn't mean the battery is bad right that instant. – Mei Oct 31 '11 at 15:54

14 Answers 14


My main APC UPS is on year 3 with it's current batteries and it's still doing fine. However, I will be bringing in a technician to run some tests to ensure that this is the case. The city I am in recently had a major power outage in it's downtown core. My UPS kept our systems up and running for 25 minutes until it was restored. I was quite impressed.

Keep up regular maintenance and have a technician look over your solution. It's a small price to pay to avoid being left in the dark.

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    This also depends on the type of UPS you're using (online/offline/hybrid), quality of the hardware, quality of the source, and other factors. A couple years is probably normal but as others have said ... you should test periodically to be sure. – Daniel B. Jun 29 '11 at 15:30
  • Having maintenance and technician running test once a year is the best thing to avoid problem. – Anarko_Bizounours Jun 29 '11 at 15:38

Your UPS vendor should have guidelines. Our APC UPSes tell us when they think the batteries need to be replaced - from memory, it's about 2 years. How heavily the UPS is loaded has a big impact on battery life. APC recommends that you never load them more than 1/2 way.


I find UPS batteries fail after 2 to 3 years of continual use. If it's an APC UPS they have a battery test function and I use this about once a month to make sure the battery is OK.


  • APC UPSes run a battery test monthly automatically; there is no need to do it manually. – Mei Oct 31 '11 at 15:48

Battery life also depends on the power quality the UPS is plugged in to. If that UPS is plugged into an outlet with really crappy power, where it moves load to battery for partial seconds quite often, that kind of short-cycling can kill a battery a lot faster than it can in a location with really good power. I can remember one case at my old job where they were replacing the battery in one of the wiring closets every 12 months due to crap power, yet the rack UPSes I was using got to 36 months old without any issues at all.

Also, cost of the UPS does factor in to this. The more expensive ones do a better job of conditioning power internally to the UPS itself which can extend battery life. Also, some are engineered to handle transient power blips or under-volts (under 200ms or there abouts) without going to battery at all.


APC says 3-5 years: http://www.apc.com/solutions/display.cfm?id=1371A38E-2B31-B5C1-CADC3E466F676960&ISOCountryCode=us

Also here: http://www.schneider-electric.us/en/faqs/FA158934/

The above is consistent with my experience of nearly 30 years in IT.


To extrapolate on Ward's comment, if you're buying UPS units on the big end of town, your UPS vendor will have a maintenance schedule to test and swap out batteries to maintain an acceptable runtime. What's defined as "acceptable" is negotiable between you and your vendor and should be tested as part of regular datacenter maintenance.


The batteries seem to last about 3 years, but I don't know about the units themselves. APC say about 4 years but I have had mine for over 10 and, apart from changing batteries, the UPSes seem to be working aok...


Remember to that some UPS can add more batteries, that will add runtime, but does not add capacity. For instance, if the USP is rated at 1500 VA, then no matter how many packs you add to it, its still only good for 1500 VA, just much longer.

APC i know has a calculator on their site to help you figure out sizing as well.

If it over loads when you put say 5 servers on it, it will still overload with 5 servers and 2 extra battery packs. Because the circuts are only able to put out so much power at once. In this case you would need another UPS and you'd want to put 2 servers on one UPS and 3 servers on the other.

  • Very good point - except you didn't answer his question. Still a good point. – Mei Oct 31 '11 at 15:52

Don't guess, test. I know it is not convenient. I know people will complain. I know you end up having to do it during off hours when you don't want to be there, but UPS operation is critical and must I repeat must be tested. Suppliers guidelines are just guidelines. As the saying goes, your mileage may vary.


My APC SmartUPS 2200, a pretty big one, that is over 10 years old and still running fine. It has built in software that monitors the running time left and lets me view it. It'll give me 30 minutes with multiple workstations and large monitors on it.

The cheap ones don't seem to last long...this may be a case where investing in a commercial class UPS is actually cheaper than replacing a cheap one every few years.

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    If your battery is still functional after 10 years, you're pretty lucky. Commercial UPS batteries tend to go 2-3 years. – Bill Weiss Jun 22 '09 at 18:29
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    I've got the same one, but the XLNET version with an extra battery pack. Original batteries and over 10 years old. It's at 50% load and when I tested a few months ago, it kept the systems running for 15 minutes and was only ~33% discharged. – Boden Jan 14 '10 at 20:42

I did maintenance work on a SMB APC UPS yesterday which is nearing 5 or 6 years old at this point. It has been running constant the whole time although it doesn't spend too long on battery. The battery runtime is still good after all the time too.

Unless you have warranty concerns, a test of the battery runtime will tell you if you need to swap the batteries. Where I work, the UPS needs to only hold load for a max of 30-60 seconds if ever as our building has a UPS. Shorts only happen when the inverter does a switch. Because of that, I'll only change the batteries whenever the warranty says so.


If you have a mission critical need then the UPS batteries should be checked often, I would be very dubious of any battery after a couple of years, i do think that some of the older kit is very well made and perhaps just by replacing the batteries will give it a whole new life


Most of the documentation I read specifies 2 years at 72*F and 1 year for 82*F.


I think it depends on the size of the UPS. At one job we had a UPS for our entire server room and we had load test ran every 6 months and I believe we changed the batteries every 3 years.

For our smaller UPS's that were at specific terminals we did not need to replace them until after 8 years.

The good news is they let you know once they start getting drained to the point of replacement so you should not worry until that happens.

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