Question Tripp Lite SU1500XLCD UPS 48v battery shuts down at 85% but voltage reads good.

Aug 23, 2016
I've had a Tripp Lite SU1500XLCD UPS for approx. 4 years now, suddenly my UPS started shutting down at 85% with almost no warning time for me to close up shop.

1350 watts
48v Battery (4 x 12v, 6 Cells)

So I bought a RBC48-SUTWR internal replacement battery pack, ironically after using a multi meter on all four 12v batteries and as a single unit I got some weird results.

My old battery was sitting at about 53.1v - 53.3v after sitting for 24 hours. (each 12v at about 13.1v - 13.6v)

My new battery (which is def different by design at least) fully charged out of the box was sitting at 51.1v - 51.3v. I charged it overnight but haven't had a chance to recheck the voltage yet and I wont be doing single battery checks unless I need to.

So a few questions...

What would cause my old battery to shut down my UPS (the new doesn't do it even with lower voltage) even though it 'seems' to have a better charge life still.

Is my new battery messed up? Is my old battery still good? Even Tripp Lite can't figure out what the cause is (big surprise lol) since the voltage is good.

My new one was running at 48.8 volts (unplugged) when it hit 50% after the overnight charge where my old one would sit in the 50-54 mark even when getting low (before the shutdowns)...while charging the new one was sitting at 54.2 almost flat, sometimes going between that and 54.4v on the LCD.

My main concern is how can I tell if my new battery needs to be returned (while I still can) but i'd also like any opinions on why my old one was acting up and still holds a good charge.

My general load is between 10-20% (highest i've ever seen on my brand new batteries), before that i'd only seen it hit about 16% while running really heavy games.

I'll be putting the old back in (again) after the new one charges back to 100% to see if any of the connectors were loose or something simple...but nobody has any idea why it could cause the shutdown and the new one does not. The Tripp Lite software says my new one has never been cycled (not that I trust it), again i'll be checking the old one soon and post the results for that when I do.

I don't know anything about batteries to be honest, just learned how a multi meter works (I know i'm doing that part right though)

Any opinions would be greatly appreciated, i'm stumped...and even though I dont mind an extra battery considering the age of my old ones, I at least wanna make sure its a GOOD battery.
Aug 23, 2016
I just tightened all the battery connections on the old battery, checked the voltage again to get the same numbers (which is really weird) since I put it back in and it got to 72 percent with just my stereo on it, on top of the charge going from 100% to 75% sitting overnight, maybe a few hours i'm guessing it may just be dead.

It handled everything but my PC (and even handled that for about 8 minutes) before it complained. It stopped beeping after I shut the PC down, but that does me no good obviously 🤬 heh.

I plan to run it on AC power and check the status in the software on this "bad" one next, but the weather here combined with my old building makes me not wanna plug it in atm, so I don't know when i'll be doing that.

Figured i'd add whatever info I could, although i'm really just trying to make sure my new one isn't Half-Dead since it was at 75% before I pulled it to test this (bad) one an it read out at 50.1--which is almost as high as the new one was when it came out of the package.

The new one after removing it again is at 75% itself an that reads off at 50.5, idk if that will improve over time but its still lower than what the old one read out as (51.9 I believe?)--right before I shut off the PC a few . ago and it stopped beeping.

To be clear, i'm using the same stuff I always ran off of it, and the same stuff I tested to see if the new one would shut off as well, but - was able to get that slight extra time that I couldn't get before removing the new one worked fine down to like 40% with my PC running so its not the box.

If I really wanna leave this simple, does anyone know what a brand new 48v should read off in DC voltage on a multi meter if its pre-charged from a factory and/or read off during use IN a UPS? (or both)

Sorry for the long confusing post, i'm guessing I need the new batty at this point for sure...but I just wanna know my new one came "new" at the least.

Again, appreciate any insight or testing suggestions, i'm passing out in my chair haha so i'll have to recheck all this later, apologize for any typos and dyslexic statements lol.

EDIT EDIT: Just ran it off the AC voltage, tripp lite software is a joke, says my old battery is zero years old and working fine lol...yet it's not.

I'm out of ideas, any suggestion on what could be causing the box to think otherwise or a way to ensure my new battery is truly new would be great, the bad one has higher voltage readings, the good one doesn't shut down the box on me. Totally confused.

EDIT: To the person who moved my thread--Sorry, I was looking for a UPS section and didn't even see this one. Thank you!
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Aug 23, 2016
Battery starting beeping at about 99% the other day...whole LCD battery bar was blinking (only on battery mode) so I yanked it since it was freaking me out to even run it plugged in like that, and I already have the replacement...UPS is over the top expensive compared to just the battery.

I'm gonna check all the wiring much closer than I had and maybe grab a battery load tester, if that doesn't give me any answers i'll likely call it dead and recycle it, or bring it to a battery shop to ask.

So this will be the last time I personally add to this thread since I thought that was an important addition...i'll leave it up until I do all that and then just end the thread, I know it's a difficult thing to speculate on without the actual equipment in front of you, but I figured it couldn't hurt to ask before scrapping a $200 battery pack heh.