Comment How to (cheaply) extend the life of a UPS (Score 1) 568
Replace the UPS battery with a car battery.
Cost: ~ UKP30 for a 60AH battery (a cheap brand is OK because huge current capacity is not required).
This will allow you to run a computer for a few hours, without braking the bank.
However, you are talking about 1KW power consumption for 8 hours - I think the only solution is, indeed, a small generator.
If you could drop the power requirement to a quarter, then a car-battery UPS solution would become practical (with maybe two or three batteries).
dny