I live in Thane in Maharashtra where we have infrequent power cuts. We wanted continuous power to run the oxygen concentrator. Oxygen Concentrator is a medical device used by people having acute Asthma and other COPD diseases.
I have got a 1500 VA inverter (Luminous "Ion" Sine Wave - 1400 KV) with two 12V Luminous batteries and this runs this medical device absolutely great in event of power failure. The back up is for almost 5 hours. To run such medical devices Pure Sine Wave inverter has to be used. Do not use modified sine wave inverters for running expensive medical devices. It was initially difficult to get hold of a good dealer but I got in touch with the regional manager at Luminous (through their website) and he suggested a good dealer. For general applications also I would recommend Luminous Inverters.
All the best.