For those of you who don’t know what a UPS is, it’s an uninterruptable power supply, or “battery backup” for your PC/servers and other electrical items which takes over when the mains fails. I have a couple of them, one for my PC, one for my server and one for my network equipment.

Recently, the batteries in one of those UPS’s decided they didn’t want to play anymore and suffered catastrophic failure. This meant that the UPS would no longer hold if the mains power dropped. Typically the batteries should last about 3-5 years but these only lasted a tad over 2 years. I was disappointed but then I began reading why this varies between UPS’s.

I have 2 UPS’s on my desktop PC. One for the monitors and one
for the PC itself. I have it this way because my PC is fairly high end so it can reach a fairly high power usage when being used heavily. A single UPS for all of this was unlikely to hold very long. These UPS’s are about 5 years old and still had their original batteries. I had known for some time these were getting poor but it wasn’t until now I decided to replace them with new ones. I have retired the UPS that had batteries die recently and took the monitors UPS and put that on my server instead. The remaining UPS for my PC now holds one of my monitors and the PC only.

I began to think why these batteries lasted 5 years and still had life in them but these others lasted just 2. I discovered that the “float” voltage, the voltage that the battery is held at once fully charged was likely too high on the UPS that recently died. It tended to hold it at 13.8v. A fully charged 12v battery sits at about 12.8-13.3v. These other UPS’s seem to pulse the power into the battery at around 13.3-13.6v rather than holding it at 13.8v. This is likely the explanation to their longer life, so it makes sense to stop using the other one and use these instead.

This discovered I decided to buy 2 new batteries, one for each UPS. I did my best to select the best brand I could because I read that they tend to last longer as well. However when these batteries arrived they were not the brand I had thought I ordered. Despite this I tried them in my UPS’s anyway and immediately had a problem.

Firstly, I checked the weight of them against the old ones. They were 0.5KG lighter which suggests a lower lead density and thus a lower energy density as well. This was worrying because I opted for the “best brand” available.

Although when I got the batteries they were not fully charged, I would have expected them to put out enough power to at least keep the PC’s online and/or boot them up. During testing they would switch to batteries just fine, but they would not start the PC from cold (powered off). This isn’t how a UPS is supposed to work, it should work both ways. During testing these batteries reached 2 minutes of sustained run time before encountering a low battery condition and shutting off. This wasn’t acceptable. The original batteries would have held the load for at least 10-15 minutes!ble. Despite that I carried on with testing.

Unhappy with this I thought I’d let them charge for 24-48 hours and see how that goes. I then tried the test again and managed around the same sustained run time. I contacted the seller on eBay that I got them from and explained I wasn’t happy. He replied saying that they are likely being trickle charged and it could take up to 3-4 days to fully charge them. The specs say 8 hours to fully charge, but they could be wrong. He assured me they were the one of the best brands and suggested I try them again in 3-4 days. He also said the weight difference should offer little difference to their output.

3-4 days later I tried another test and managed 12 and 14 minutes between them. This was significantly better but not quite what I expected. I contacted the seller again who said it might take a couple of charge/discharge cycles to get them to 100%. I agreed as batteries do sometimes need this cycling so I said I would try again in a few more days. It’s only been 2 so I haven’t tested them yet, but I am hopeful that they will be slightly better again.

All in all it’s been a bit of a pain but it was also a learning curve involving a fair amount of research. This leads me on to my next blog about battery knowledge, as I have learned a few things I didn’t know about how to care for batteries recently.