Curious what prompted the new battery?
By far the most drastic "mod" to increase range in an EV is simply driving slower. I know you'll probably get run over in CA if you aren't bumper to bumper with the guy ahead.
Weight isn't going to make much difference; not measurable anyhow. Your range savings by weight reduction is going be feet, not miles.
Use seat heaters instead of cabin heat; seat heating is very efficient.
There might be a tiny benefit replacing the 12v battery with a LiFePO4, but only if it doesn't get exposed to freezing temperatures.
Aero treatments mentioned by Ecky are the next thing on the list after simply driving slower though.
Here's the other thread on the i3;
https://ecomodder.com/forum/showthre...ics-37645.html
Bob Wilson also had (has?) one.