Help my computer work during power failure

I am home user and use my system daily upto 10-15 hrs . My problem is the area I stay suffers from severe power cuts daily for 5 - 6 hrs. Though not continiously but in a gap of One and half hour or so.

I have an UPS presently connected ( 600 va Xe-Bac)

it hardly gives me backup time of 10 mins.

My question is

1. Can i increase my backup time of UPS. Say 3 Hrs ???
2. Can I connect a DIGITAL SINE WAVE INVERTER to my system ? if so please mention the company with price (approx) and batt. specifications along with the VA needed for two systems with 15 inch monitor. ( for future additions...if i add one more system )
3. Will my Computer suffer any problem if I go for an Inverter ?

what risks and benefits will involve in this procedure ??

plz help me by replying ////////thanks

[enoonmai]

If you wish to increase your backup time, the only way to do it is to get a UPS with a higher rating that can sustain your system for at least 30 minutes. All major UPS manufacturers provide higher ratings UPS, but be warned that they are costly. As for connecting inverters directly to the system, well, I am yet to hear of someone doing that, although I would suspect that you MAY end up with problems if the output isn't pure enough. So it would probably be wiser to invest the money in a higher quality UPS, in my opinion.