the computer UPS is desiged to safely allow the computer to shut down, its not designed for hours of run time.
some may last for 10 minutes. a desktop computer takes about 150 watts the batteries are about a 90 watts so you can see it would last about 25 minutes, it signels the comouter thu a USB port to tell the computer to shut down as soon as it can.
what you need is a system that has a deep cycle battery used in the solar industry known as a AGM battery, at 12V 150 AH battery is comon, this equals 1800 watts. then you need a inverter to change the 12 volt DC battery to 120 volts AC to operate your equipment.
you need to look at the label on your equipment to see how much power it takes it will say it takes 120 vac at 2 amps
or whatever, then to convert to watts you mulitply 120 x 2 = 240 watts, this will tell you what inverter to purchase. if it is 240 watts then purchase a 400 watt inverter, cost about $60. Then you need to recharge the battery with a battery charger.
a standard battery charger is only good to charge the battery and not keep the battery charged up during non use.
so you need a special battery minder/charger.
here is a idea of a product that may do the job but you need to know how much power your device takes
this one uses a 12v 60ah battery = 720 watts, but you can only deplete the battery to 60% = 400 watts
so if your at 240 watts you less than 2 hours but 24 watts would be 20 hours if thats your case.
the main problem with this product is the recharge time it says 15 hours - that just nuts
you could get a 40ah battery charger then it would take 2 hours using a power generator
http://www.amazon.com/Xantrex-802-1500-XPower-Portable-Powerpack/dp/B00005RHQQ