Perhaps some of my previous comments on this matter are appropriate: Boeing is a marketing company not an engineering company. Saving weight with lithium cobalt dioxide batteries packed cheek by jowl saves space for more marketable and fee generating cargo and slf amenities which contribute to shareholder value. The stock market forgets much more quickly than the families of a few dead passengers. I suspect the electrical system weights and redundancy decisions were made by MBA's, which like papal pronouncements in catholicism, are infallible in the corporate religion. No need to get your hands dirty (yecch!) with the actual physics and you can always wear a suit and look corporate.