If it?s a local ups, then you need to check its adjustment. I have recently also bought an imported ups ?mercury? and feels satisfied with its factory set adjustments, only thing required with such a ups is good electrolyte from very first day. Coming back to your question
- You did not tell us about the AMP-Hr ratings of your battery as charging rate depends upon that. As you said that it worked fine for first two years, so most likely battery must have lived its useful life. Battery life does depends a lot on quality of electrolyte used and UPS adjustments, once batteries gets old then you need to decrease its charging rate in-order to extract the remaining juice out. Like you said that it completely charges in 20-30 minutes on 12-14 Amperes of current so by reducing the charging rate to 4-5 amperes, you will be able to extend the backup time and use it till it finally gives up before buying a new battery.
- Lower end cutoff voltage should be adjusted to 10.3 Volts maximum, like your drops to 8-9 Volts so that?s an abusive factor on battery. So damage must already be done but get this adjusted before buying a new battery.
- C.G in all the cells looks good except for one which had 11.3 C.G. you don?t concentrate the gravity later as drop in C.G in one of the cells point towards the problem area.
Follow these steps as well, as C.G in all the cells does not looks bad.
1) Reduce the charging rate to what I have told you.
2) Then once it fully charges its self then observe the back up time, sit with the battery with a voltmeter connected on battery terminals and observe how fast battery discharges its self. Like if it remains stable till 11.5 Volts for example and then starts rapidly dropping then that clearly shows it times to get a new battery.
3) If this drop is not rapid then most likely the flush will be useful.
You can also experiment following on the battery but that?s an experiment
1) If ever, everything points towards that flush will work then make preparations for preparing a new electrolyte or if ever you want to buy it.
2) Prepare the solution of espom Salt by using the directions from internet and put it into the all the cells.
3) Let it charge and discharge while its connected to the ups for few days.
4) Meanwhile use this time either to buy a good electrolyte or prepare a new electrolyte.
5) Flush everything and pour new electrolyte in the battery.
Only if you can afford this hassle.
P.S: quality of electrolyte used does makes a lot of difference
