It is not easy to (make a "bigger fuel tank") with a battery.

As battery technology improves, more energy storage can be packed into the same space.

Let's take a current 3000mAh rechargeable Li-ion AA battery, vs older 2000 mAh versions in the same format.

If you look even further back at older tech NiCad batteries, those topped out at 1000mAh for AA's

Now whether your vehicle's charging electronics can handle the greater capacity, much less different battery technologies, that's another story.

I would love it if I could drop a shiny new semi-solid-state battery into a used EV, and gain all the benefits.