Luna designed their wolf pup battery to mount under the down tube right next to the motor. It mounted with velcro straps, no eyelets, and was a pretty small battery. Seemed like a good spot for that battery.
I don't think there is a safe place on a bike in the event of a wreck. Seems like every bike wreck I've ever had spread debris over 20 square yard area. I think Luna's potted batteries have a real advantage in the event of a hard fall. Can't imagine hitting so hard the one would spill batteries.