battery size for a UPS depend on max load & duration for which a UPS is required to be used.
For a 700 watt UPS / 220 V AC - for 7 hour battery operation - you need ....calculator ! using following basic rule.
The current I in amps (A) is equal to the power P in watts (W), divided by the voltage V in volts (V):
I(A) = P(W) / V(V)
A= W / V