Save Money on UPS Batteries by Using Cheaper Ones With the Same Voltage

I just got (another) uninterruptable power supply (UPS), and it didn’t work.  The fix was the replace the battery.

New UPSs are $50 and upward, well into the $200 range, for the household type. You can save a few dollars by purchasing them non-working, and replacing the batteries.

The trick here is that some UPSs, especially the cheaper ones, have odd batteries that are extremely expensive. You can replace the batteries with larger, more common ones, as long as a few things match:

  • The voltage needs to be identical.
  • The technology needs to be the same: VRLA or valve regulated lead acid, and absorbent glass mat.
  • The connector needs to match. More on this later.

If your UPS has cheap batteries, then, you’re home free. Just buy them and get on with life.  However, the rest of the article can help if you want to test your UPS.


Most of the small UPSs I’ve seen operate with 12 volt batteries.  This can be a single 12 volt battery, or a pair of 6 volt batteries.

UPSs have a little computer inside that checks the battery voltage, and charges it up if it’s too low. If the battery is dead, it won’t attempt to charge it.

I used to think that all UPSs would always try to charge the battery, and put 14 volts across the terminals, but I was wrong. A recent UPS didn’t put any voltage across the terminals until I installed a working battery.

My guess is that it tests the battery and refuses to charge one that’s dead.

How can it tell?  Well, generally, a dead lead acid battery has 1 volt across the terminals, and a discharged one has around 2 volts across the terminals.  Maybe it checks the voltage, and refuses to charge when it’s too low.

So, the first way to see if a UPS will work is to put a functioning 12 volt battery into the system.  The easiest way to do this, is to have two similar UPSs, so you can swap batteries.

If you can’t swap, you can buy a fresh battery. It should cost around $25 to $30 delivered. Search around online.

Another way is to hook up the UPS to a 12 volt car battery. You can search for that on the web.  Given the hassles of dealing with car batteries, I think it’s cheaper to buy a battery.  (You could spill some acid and destroy your clothes or carpet.)

Connectors: F1 and F2

The most common UPS battery terminal size is F2, but, sometimes, the UPS needs an F1.  The F1 is smaller than the F2, and you can get an adapter to upsize the F1.

The F1 is 3/16″ wide. The F2 is 1/4″ wide.

Get a Battery that’s Close Enough

I had a cheap CyberPower UPS, and the batteries were expensive. So I found a cheaper battery that was the same voltage, same connectors, and just a little bit bigger (so it had more capacity).  It worked.

I just had to remove some plastic from the case, and then use tape to hold the battery in the  UPS. It works fine.


The two main low-cost brands are Belkin and CyberPower. The main premium brands are TrippLite and APC. I’d go with the cheap brands, mainly because all their stuff is generic. APC is well known for having weird connectors, and doing tricks like custom serial cables to generate more profits.

Where to Buy?

I’ve bought them from Craigslist and Ebay.

I’ve also found them at thrift shops, but didn’t buy them.  I would consider them, now that I have an extra UPS.  The main problem is that the only ones with a good return policy are Goodwill, with a seven day return, but that’s not enough time to get a replacement battery.

On Ebay, filter for “For Parts or Not Working”, and read through the ads. Some will say that it works, but the batteries are out.

The batteries are a big expense, especially for the cheapo units, and, sometimes, people will sell the old unit and upgrade to a new unit when the battery dies.

The best thing to do is make sure they all  use 12 volt batteries.  Then, if possible, all use F2 connectors.  Once you have that standardized across your network, you can always swap batteries to test.

What’s a UPS Good For?

It can keep the Internet connection up during a power outage or brownout.

You need to put your cable or DSL modem, your router, your switches, and your phone adapter, on the UPS.  Your laptop already has a “UPS” in the form of a battery.

When the power goes out, your laptop stays on, and all the network stuff stays on!  It’ll stay on for several minutes.

What you should do is take the time to save your data and close apps. This way, all the “Internet” stuff is done, before the connection runs out of power.

I use Thunderbird email and can “go offline” by downloading all my mail, and then working without the Internet.

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