Like everybody said, you can use any cirtcuit diagram of any inverter and adapt it to the one you need by using high capacity batteries, powerful transoformer and using more transistor for driving more current, you can also use any UPS schematics only delete the input stage from 220V
you can find schematics here:
http://www.sonsivri.com/forum/index.php?topic=1277it is very simple but effective, only be caution it is working under 14V so you must change some component like capacitor and resistors, vereything else should be fine.
best regards