Battery Upgrade for Evolve BGTR

So yesterday my BGTR ran out of juice about 2 miles from my car & on the walk back it got me to thinking about more range. My knowledge of batteries consists of storing them in the fridge, so I am posting my question here:

I love my board I just want to get a little more range out of it. A little more speed would be nice too but I can get (part way) there with gears & wheels so increased range is my top priority.

Am I better off buying an extra (stock) battery to swap out OR can I go DIY/Custom to build/buy a superior battery that will be compatible with my BGTR? A new battery from Evolve runs $650 - Any idea what I would need to spend to create/commission a custom battery w/better range?

Will this require upgrading the motors or electronics?

All help appreciated - thanks