I have a 4kVA UPS(uninteruptable power supply) I found it at a ham radio swap meet and paid 50 dollars for it. It has a digital readout of AC volts in/out, %Load, battery voltage, runtime. I used it for about 6 months and now it needs new gel batterys. There is 2 12 volt 32amp hour gel batteries hooked up in series for 24 volts and I don't want to spend over 100 dollars replacing them. I hooked 2 deep cycle lead acid marine batteries(about 2 years old) and the UPS seems to work fine, I unpluged the AC cord and at 40% load it ran for almost an hour before the 5 min alarm sounded at 22.5 volts so I pluged it back in. The charging circuit shows full charge at 27.4 volts. My question is can I keep using lead acid batteries to replace the gel batteries? Will it destroy the batteries or kill the UPS?