Hi, Ive been looking online at UPS systems and I have noticed that many will only run a system for a couple minutes, is it possible to add extra batteries is parrallel and extend the run time of your system? 

a ups is only meant to 

A. safely shut down your computer


B. provide a smooth bridgeing to a backup generator

There are plenty of UPS's that can keep your computer on for several hours, but they are very expensive and quite big.


You can have parallell UPS configurations but they need to support it, you can't do it with any model.

Yes it is possible but there are of course issues:

1) there are high currents involved meaning you need adequate (thick) wires and fuses on each battery,

2) because you are extending the time UPS has to provide power there is high probability that it will heat above acceptable levels and shutdown or burn before discharging the batteries - having UPS rated for 2-3x power needed will definitely help,

3) recharging the batteries is now going to take days or even weeks,

4) lastly if you had to ask then you probably shouldn't do it - for safety reasons.