PC Hardware → Testing battery backup with car battery?

I have a Tripp-Lite 1000LCD battery backup (I will call it UPS for short) which I recently removed from service because I think it is bad. About two weeks ago I twice found the computer had powered off suddenly and found the UPS off also with no warning and no power failures. I suspected the battery was bad because I had this happen last year due to bad battery (3 years old at the time).

But since this was relatively new battery I was not convinced it was a bad battery. So I dug up an old MinuteMan MN525 unit that only needed a new battery and put the battery from the Tripp-Lite and it worked, so I dismissed the battery as bad and put the MinuteMan back in service with my computer.

Fast forward to 10 minutes ago. I decided to do a real test with this battery by unplugging the UPS from wall and looking with a stopwatch how long until the battery died. Well, the thing lasted less than 2 minutes. Not enough time for a controlled shutdown given that I usually wait a couple of minutes before powering down if there is a power failure and even worse considering that this MinuteMan unit cannot tell the computer the power is out (legacy serial connection I no longer have). The same battery lasted 33 minutes in the Tripp-Lite with the same computer hardware when new on a similar test.

I now suspect the battery is actually bad but I am not sure if the Tripp-Lite is bad also. My suspicion is that the larger 1000 VA transformer in the Tripp-Lite (vs 525 VA in the MinuteMan) is causing too large of a voltage drop in the battery that it simply shuts down. I have no other battery to try. The only battery that I could connect to the Tripp-Lite is my car battery since it is the same type of battery and same voltage. But..... is it safe? I only need to connect it while powered off then try to turn it on. It should turn on if the unit is working fine.

For a test, it's most certainly safe (I'd take other steps if this becomes permanent). If you want to be extra cautious, get an inline fuse holder from Walmart or your favorite auto place and stick a ~30A fuse in there. The transformer could technically draw ~100A of current on the DC side but I'd bet the DC wiring is no larger than 12-10 AWG (IOW, not large enough to reliably handle 100A, especially from a battery that can provide MUCH more). There should be an internal fuse in the event something goes wrong but this just provides yet another safety measure and is one you know will be there instead of assuming there is one inside (and if it does blow, you hopefully won't have to open up the case).

FWIW, yes that battery is pretty much dead. Chances are it was shutting down due to a self-test (usually happen weekly or so). I'd doubt the Tripplite UPS is actually bad and you could just replace the battery knowing that even if the UPS is bad, it will still work in the MinuteMan UPS.

The UPS system do go bad too, I through away 2 x APC 350 ES this week. I had assumed the batteries were bad, replaced them, still bad. I tested the batteries I took out of them in another UPS, they worked fine.

I have found the batteries usually live for about 4 years.

It's safe as long as you use an inline fuse to limit the max current. While it's not very likely, it's possible that the UPS has a short somewhere and if you combine that with a battery that can easily source several hundred amperes, that may lead to the release of some magic smoke.

Haven't tried this yet. Haven't figured out how to go from a set of standard jumper cables (safest and easiest way to connect on the car side) to the smaller wires in the UPS.

And yes, I am guessing the UPS has 10 AWG battery connectors. Those wires are bigger than what is in my house 120 volt outlets.

Because at lower voltage you need a higher amperage for the same power, and for that amperage you need a thicker wire.

The cables inside the UPS will have female end spade terminals (usually F2 size, 1/4" I believe) that connect to male variants on the battery. Here's what you need:
- a set of male spade terminals (the yellow 10/12 AWG variety)
- a crimper (can usually get the crimper with a small collection of terminals together)
- a section of 10 AWG wire as long as you need to make a pair of leads (probably a few feet for each lead)

Strip the ends of each lead, crimp the male terminals on one end of each lead leaving the other end bare. Plug the leads into the corresponding leads coming out of the UPS and use the jumper cables to bite on to the bare end of the leads. Alternatively, you could get battery terminal clamps for the other end of the leads and skip the jumper cables altogether, connecting for UPS directly to the battery.

This does also leave out the inline fuse. I left it out as it seems like this is getting complex enough for you as is but you should really have it in there for your own protection. If you'd like I can draw up a diagram of how to put all this together and even give you links of what to buy (everything can come from Walmart).

I know how to connect it electrically. No issue on that part. It is the physical part. I could do the spade terminals and crimping, no problem but it would be too much of a trouble to set it up for a test that will only last a few seconds and given the fact that I don't have the terminals or the tool. Will see over the weekend if I can put something together. I only need to see that the unit will start with just the battery as it is supposed to turn on while unplugged if the battery has enough charge. If it does I know the unit is fine.

Will probably go ahead and get a new battery to test as JoelC707 suggested. The battery in the UPS is bad anyway and if the Tripp-Lite is bad I can still put the new battery in the old MinuteMan unit.

Ok, the end of the story. I went ahead and purchased a new battery. I had the Tripp-Lite unit with me in my car and just out of the store I put the new battery in and tried to turn on the unit. IT WORKED!!! The not-so-old battery was bad after all.

Great news! Out of curiosity, how old is this "not-so-old" battery? Maximum service life is 5 years tops usually with typical being 2-3, maybe stretching to 4 years. Service life really depends on how often the battery is cycled, they can only take so much, but never being used and sitting on a too-high charge all the time will kill them too.

The not-so-old battery was purchased on August 10, 2013. I found out it was bad about 2 weeks ago, a little over a year after I installed it. The original battery from that UPS lasted about 2 years and 9 months which is about on par with what my car battery lasts. Last year I found it was bad after I was away from home for 2 weeks (and therefore UPS off) and when I returned started seeing the sudden powering off of the UPS, just like I saw 2 weeks ago.

In terms of usage, the UPS is always on but the computer is only on for part of the day. The only constant load are the cable modem and router. Only the computer, monitor and network devices are on the battery backup side. The UPS is off only when I leave home for more than 2 days or if there is a power failure lasting more than a few minutes (and I am home at the time to turn it off to avoid battery discharge).

As an interesting twist to this story, I also replaced my car battery today. It will be interesting to see which one goes first in 2017 if I happen to still have both of them by then. I predicted my car battery was due for replacement in August based on the life of the previous batteries and the prediction came out pretty accurate. It didn't die suddenly but today it was the first time I was afraid my car would not start so I went and changed it before it actually died.

That is, IF the new UPS battery won't fail prematurely next year.

Do NOT use a car battery.

They are meant for bursts of power, you need a deep discharge battery. At the least a car battery will give you mixed results.

Also I have never had a 12v SLA battery spark on connection, car battery more than once.

»en.wikipedia.org/wiki/De ··· _battery

Read the entire thread. It was just for a very short test, to see if the UPS was able to power up on battery alone as it is supposed to do. But it is pointless anyway because I ended up buying a replacement battery for the UPS and it worked. I never did the test with the car battery.