UPS Charging/Full Cycling

Local UPS. 500W. Used to run a couple of fans/lights. Working fine but exhibiting different behaviour.

Earlier, when it was charging -- the charge indicator came on and after it was charged fully, the charge indicator went off and the FULL indicator came on.

Now -- after it has charged fully, the charge indicator goes off and the FULL indicator comes on. BUT, after 2-3 seconds, it goes into a cycle. The FULL indicator goes off for a split second, the charge indicator comes on, battery charges (all in that second or so), then charge indicator goes off and FULL indicator comes on. Has been doing so continuously every 2-3 seconds. Don't know much about UPS's. Battery fluid level seems fine.

There could be either of these two problems

1) Full charge detection circuit got some problem.

2) Battery is getting old and unable to hold it's full charge voltage.

Do you have a voltmeter ? If yes, can you measure battery voltage when

3) Full charge indicator is ON

4) When full charge indicator is off and charging light turns ON ? Does battery terminal voltage start increasing then ?

I want to know the difference in battery terminal voltage between "Charging" and "Full Charge" indications

Edit: Check your battery terminals for any signs of corrosion and if they are not loose.

Check the charging indicator wires for loosing. Does your UPS hold the load whenever there is WAPDA breakdown if it is ok then surely some loosing in the wires/circuit.

The cycling problem seems to have gone away for the time being. Possibly a case of loose connection. Though, it does seem that even with a fully charged USP, the fans now run a bit slower than before. Maybe, the battery might be failing also.

If the problem isnt't solved, I will try to figure it out in the coming days. In any event, thanks for the advice and possible causes. Should come in handy in getting to the root of the problem.