When I have trouble getting the regulator to allow me to approve the installation of an instrument with an internal battery, because I cannot demonstrate the inherent safety of that battery, we're a way's away from the regulator being comfortable certifying a primary power battery bank. We'll get there for sure, but it's not just around the corner....
We need new redesigned regulators for the future too. Why is it OK to have filthy and noisy petroleum engines that catch fire and blow up on a regular basis. Fuel starvation is an enormous contributor to fatal accidents. We train our pilots to treat the fuel gauges with extreme caution. Most gauges rely on a sender that is exactly the same as those fitted in my toilet cisterns. We live with all these dangers though because of the benefits they bring. Everything has its price.
I'm reminded of a PPL who told me that he had owned aeroplanes for over 40 years both new and second hand but he'd never owned one that had all things working. I remind my students, all the time, that reliability is rarely underwritten by regulation. The regulator requires predictability. In the modern world technology advances so rapidly that by the time predictability is established we're onto something new and the cycle begins again. The regulators forever playing catch up do not deserve disdain but they struggle to overcome their inbuilt prejudices. They are to put it simply not very keen on change.