Back-UPS Pro 1500 (BR1500G) won't stay charged after battery replacement

[Anonymous user]

At 6 years-old, the batteries in my Back-UPS Pro 1500 were significantly degraded (less than half of capacity at new), so I ordered replacements a few months ago.  Shortly after they arrived, we had a major power outage, so I swapped them out while the power was out (everything was shut down anyway).  I charged the unit for about an hour right after the battery swap on a square-wave inverter since I wasn't sure when power would be restored, but it ended up being restored the next day.  When the power came back on, I thought everything would be fine, but the batteries were soon after showing that they were draining instead of charging.  After hooking up Power Chute, setting the battery replacement date, and doing a self-test, they were charging again, and eventually reported "charged".  The next day, however, the batteries were almost dead again.

I tried to reset the unit multiple times (holding down the power button with the unit unplugged) and reset the battery replacement date in Power Chute again afterwards, but nothing fixed the issue.

After opening up the case and connecting a high-quality volt-meter, I finally determined that the batteries will be charged with a steadily increasing voltage up to 27.4 VDC, and then held at 27.4 VDC for about 8-12 hours, before the UPS stops applying the "float" voltage to hold the batteries charged.  From there the battery voltage would drop all the way down to about 24 VDC, when I would finally step in and get them charging again by either unplugging, turning off and back on, or running a self-test.  All of these methods put the UPS back into charging mode (which is by design) and everything is fine again until the unit is again fully charged.

After talking to APC Technical Support, they agreed that it seemed like a mis-matched set of batteries.  They sent me a new set, but the new set yielded the same problems.  I tried the same reset techniques (hold power button down with batteries unplugged), but this didn't clear up the issue.  I now have a UPS that still works, but has a constant discharge-charge cycle that has to be manually performed by running a self-test twice a day.  I'm figuring I will have to just replace the unit, but I figured I'd ask here to see if anyone had any ideas of what could be wrong and what I should check to see if I can get this unit to simply hold the charge once it's done charging.

I don't know if charging the unit for an hour on a square-wave inverter would have caused this issue, but I'm not sure why it would have.  The unit reported a "wiring fault" during this time and I wasn't running a load off of the unit because of that.  I had another, smaller and cheaper APC unit charging at the same time and it suffered no ill effects.

[Anonymous user]

I have the same problem with my BACK-UPS Pro 550. Very frustrating. APC wont do anything

[Anonymous user]

Agreed.

Now I have no choice but to throw out an otherwise working UPS after having bought a replacement battery.  This UPS worked fine until the battery change and now it's toast...

I was hoping someone would have some input on what to look at.  Maybe even a part to replace.

[Anonymous user]

I have seen some reports here of capacitors failing in some models. You may want to look in the unit for swollen and leaking capacitors.

[Anonymous user]

Thanks for the idea.  I'll take a look at that this evening.

[Anonymous user · Accepted solution]

I checked that evening, but never posted back.  No obviously damaged capacitors.  (No puffed up tops on cylindrical ones and no puffed out sides on disc capacitors.)

Guess this thing goes into the trash...