Not a stupid idea at all. Battery upgrades are one of the more common ways to get more range, but the details matter.
From a battery pack perspective, I’d first look at the original voltage, Ah/Wh, available space, controller current, and BMS rating. More capacity at the same voltage usually means more range, but changing voltage can get complicated because the controller, charger, display, wiring, and connectors all need to be compatible.
Also keep weight and mounting in mind. On an off-road bike, vibration and pack security matter just as much as the electrical specs.
What model bike is it, and what battery/controller setup are you running now?