David,

You cannot guarantee a power supply won't fail by fitting 2 batteries but you can reduce the likelihood of failure. The ETOPS aircraft you talk about are not free from failure either as proved by the 777 with the double engine failure at Heathrow. The design of these aircraft is to an acceptable limit of failure.

If you think the Weatronics makes solves all your problems then you are wrong. Admittedly it does reduce the chances of failure but doesn't remove it completely. I have looked at the Powerbox RRS for twin receivers and that introduces numerous extra failure points too.

Each person chooses the level of risk that he is happy with and your direct patronising comments so soon after such a disastrous incident does you no favours.