1) NS 175 battery would correspond to roughly 150 AMP-HR rating where as charging rate is set to 14 Amperes which is perfectly fine.
2) You mentioned that cut off Voltage is around 13.9 Volts to 14 Volts which is also right
3) Rating of your UPS is 750 VA which implies that it is should be off 1000 Watts and can also handle small inductive load, so good enough.
See your charging rate is fine and set to its allowable maximum limit, due to intensity of load shedding we cannot reduce the charging rate as we want the batteries to charge its self in smallest possible allowable time. This maybe the reason that you see battery caps black from underneath, nothing to get worried about if what you are telling me is right.
Problem you quoted was related to the gravity of the batteries and you said that batteries were new. I don?t exactly know concentration of sulfuric acid in Electrolyte once it was prepared by the battery shop in start. They do the rough analysis and most of the times its not correct. Its also important that electrolyte be prepared with distilled water and distilled water be used later to top up the batteries if you want your batteries to last reasonably long.
Maybe bad dirty electrolyte is contributing towards killing the batteries earlier if gravity in start was ok or it can be less concentration of sulfuric acid in electrolyte right from the start. Anyway, if that?s the case then you can prepare a bottle of electrolyte with 1400 gravity or buy it from market, remove some electrolyte and try to put the one bough in order to bring the gravity near 1230 -1240.
Anyway, you guys find it hard to perform flush or prepare new electrolyte with distilled water but had I been their then I would have performed a light flush and filled the batteries with my own electrolyte for long lasting life.
Sorry, I am not a shop keeper but always want to see my equipment performing in top notch condition that?s why I take some extra pain and then enjoy long lasting comfort from my investment.
