Buying an 1 KV inverter. Is my existing 12v 200AH battery ok for it or do i need a 24v battery.?

I assume that you are purchasing a 1000 watt (KVA) 24 volt DC input to 120/240 volt output inverter. If so, then yes, you need a 24 volt battery or two 12 volt batteries wired in series. I would think that two 12 volt batteries would be more practical.