“reduced the size of the batteries”
That’s the holy grail. Not so much physical size, but energy density. It’s been worked on for 40 years and fundamental chemical limits have not allowed much improvement in kWh/lb. It’s not like batteries are only half as good at storing energy per pound as hydrocarbon fuels. They store only about 1/13 the amount of energy per pound as hydrocarbons. Billions and billions of dollars have been spent on this with little to show for it.
I wonder if they could use a flow battery? If the electrolyte is non toxic the could discharge it as they go. It could also be pumped aboard for refueling on the ground.