thanks for suggestion, can you please share some of the commercial unit Links . I am going to use this for in schools in India. as there is a powercut in remote areas so that why i am looking for some rechargable battery assisted power supply.
Then for anything to do with batteries I would stay well away from DIY, unless of course you are an experienced electronics engineer. And for the rest of it you do need to understand the safety implications of what you are building.