Apple is developing hollow batteries for it’s new automobiles. This is for thermal management I expect they will be placed around coolent tubes. If you want a coherent beam in a flashlight the longer the reflector the better the beam. So you could place the reflector inside the battery running the entire length of the battery.
I read this today too. With Tesla building the largest lithium battery production facility in the world outside Reno, Nevada, I expect big changes in production and design of battery technology.