My trusty 30 year old APC Back-Ups 280B acts like it's working... until testing/no power

[JOHN_FL]

I have an old Back-UPS 280B.  It's worked quite well for a long time.  However, (not necessarily lately, I can't say exactly when) I finally realized, it's not keeping my router/cable modem powered in the event of a power outage.  (I suppose I'm fortunate to have few enough outages that I never really noticed.)

The power light on the switch no longer lights up, but it does function.  It beeps when I turn it on.   ANd, if I go into test mode or unplug it, it does it's cadence of a beep every second or three to tell me power is out.  But, whatever is plugged in won't have power while in test mode or unplugged.  And the unit is keeping the battery charged.

The battery seems good.  On the multimeter it's a solid 12.72 volts, no fluctuating.  To be fair, it's an old-ish battery, but as far as I can tell it's in good shape.  I'm in another catch 22 of "if I have doubts about the unit, do I want to buy, and possibly end up stuck with a new battery I won't need if the unit is bad?"   The battery did power a lamp through an inexpensive 12 volt inverter for ten plus seconds, showing 11.34 volts while running the inverter.  Assuming I only have an inexpensive multimeter and nothing much beyond that, is there a better way to definitively test the battery?

I have another amusing mystery;  There was a 5W15OJ (rectangular/white)  resistor rattling around loose in there.  To the bet of my capabilities, I would say that it belonged in the R99 slot on the board, but I can't say with certainty.  I can say that carefully positioning and holding it in place while testing didn't make the UPS work.

So is it the battery, or is there some other likely failure point?

[Teken]

John,

Short Answer: Replace Unit

Long Answer: The battery is not healthy and needs to be replaced. This is superseded by the fact the UPS needs to be replaced given the broken resistor.

There are dozens of UPS options available that cover the entire spectrum in terms of price. 

Take this opportunity to splurge on your self and buy a pure sine wave inverter made in 2024! 👍