CS 500 (BK500EI) runtime limit - with external battery

[Anonymous user]

Hello everybody.

I have purchased recently a used but working APC CS500 to power my 220v water pump during a blackout. Since the ups has no warranty, I removed the old battery (dead anyway) and hooked up a 12v 12Ah lead acid battery to test it. Using a multimeter I have managed to measure the amps drawn from the 12v battery when the pump was in use (around 10 amps). I have tested the runtime of the ups with this set up, and it kept powering the pump constantly for about 40 minutes untill the battery was depleted (the ups shut down when the battery was 11.5-11.8v, I don't quite remember).

So far so good. My biggest concern, that ups's are designed to provide power for only a couple of minutes (untill you safely shut down your computer), was gone.

Next, I removed the 12v 12Ah battery and replaced it with a new 12v 140Ah deep cycle lead acid battery, and according to my calculations it should give me a constant runtime of minimum 7 hours. The problem is that the ups shuts down after exactly 100 minutes and I have to power it back on to give me another 100 minutes and so on. 

I do not have the PowerChute software installed since I do not have the special 10 pins Rj45 to Usb cable.

My question is: 

If I decide to buy the cable will I be able to modify this setting? Either to disable it either to a minimum of 360 minutes?

Thanks in advance for your answer.