a 24V ups is always a better circuit than a 12v. it would be useless to save 2000rs over a ups and burn through loads and batteries on yearly basis. always invest in a bigger better ups now, and buy smaller batteries now.. invest in bigger ones latter.
PS: for 16k ups, simtek isnt that big a brand or a better performer. price for performance is too high.. plus all desi ups have a very low cut off value going to 11v or even lower sometimes when battery is older leading to excessive discharges and overcharging.. you might wana look into APC or some better pure sinewave inveter in that price with warranty..