Assuming it is antimatter-based you can double that capacity by consuming air. But that just turns it into a fuel tank for an internal annihilation engine and hardly qualifies as battery anymore.
The answer is really, really good. Fast charging, long rang, 1 million mile lifespans.
Add on top of that the ability to connect into a smart grid and earn money by buying energy off-peak and selling on-peak, and the ability to double as an emergency generator for your home.
Why not? There are plenty of battery technologies that use air as an oxidizer.
> battery: a container consisting of one or more cells, in which chemical energy is converted into electricity and used as a source of power.
> cell: a device containing electrodes immersed in an electrolyte, used for current-generation or electrolysis.
An antimatter reactor would not be a battery because it would not contain any cells. Additionally, because it converts nuclear energy into useful power, not chemical energy.