[JRC] Emergency Power

[Fabio IZ4AFW]

Hi all,
    I am planning to add emergency power to my ham station. That is a 
long-term project, so I have no hurry.
I was thinking about some batteries (maybe lead-acid ones) and a homebuilt 
battery charger to keep them charged.
I live in a city and power outage is not usual, so I just need emergency 
power for some hours, just in case something serious happens.
My VHF works on 12 V so I think I won't have big problems here.
Now, the problem: the only rig I have for HF is JST-245, which of course 
runs off 220 volts AC, so I think I need a rather big (and expensive?) 
inverter.
At full power (TX) the '245 is rated at 900 VA if I remember correctly, but 
if I use it at about 100W output I think a 600/700 VA inverter will be enough.
Will I need a pure sine inverter or can I live with a cheaper one?
Thanks for any suggestion and comments,
73
Fabio IZ4AFW