Try disconnecting the smart cable and the AC cord and let the
UPS run under your regular load until it shuts itself down.

There appear to be two different runtime calibrations, one in
firmware (which the above addresses), and another in software.

See Option 3 in
http://tinyurl.com/6yjdn

wrote:
Greetings:

I have an APC SmartUPS 1400RM that I just replaced the (now dead)
included batteries with a pair of 75AH deep cycle marine cells (L/A)
hooked up in series (24V system). At 48% load my runtime is
rediculously small (It's showing me 0 minutes right now)... I've run a
runtime calibration on the UPS, but that doesn't seem to have
helped... Doew anyone have any suggestions, or is this truely the kind
of performance I can expect?...

Thanks,
Richard W.