I have designed many circuits for inverters but I can say the circuit used in exide EX850VA is the best of all .
It gives pure sine wave output regulated to 220 volts .
It uses the latest technology to convert DC to AC also charging circuit provides continious DC current which ensures long battery life and genuine backup this is a digital inverter so we can check what the charge remains in our battery , what is the load % , also the input voltage. A genuinely recommend this to all of you.