Which inverter to go for?

I am in need of having computer backup (apc powerchute shows around 200W usage) for at least 8-12 hours for my work + a fan + a fluoroscent tube.

(planning to get a pure sine wave one)

What inverter rating and battery rating should I go for the above setting? 800va + 1500 ah?

Suggestions needed in battery. which exide variant shall I go for?

regards