Batteries were always a pain, and no matter how good you are at remembering to charge them up, you will always mess up once in a while. I'll be sticking with the mains supply.
Is this a case of 're-inventing the wheel', as it were, selling us something that we don't really need? I mean, we have batteries and we have mains supplies. Now some bright spark has thought up the idea of a rechargeable battery that you can plug into the mains so you can use it and charge it at the same time. Brilliant.