Ruh roh.
I hope you get that sorted out. That doesn't sound normal. Might want to get a battery replacement under warranty.
My 2015 IZIP E3 Dash used to indicate 47 miles of range when I first got it. After 100 miles, that dropped to 43 miles, and at 600 miles it dropped to 41 miles, and now at 2,000 miles it indicates 38 miles.
The good news is that IZIP has used this 48V 417Wh battery for years, so I imagine it'll continue to be available as a replacement part for years. I asked Steve at the IZIP Store in Santa Monica about the price for replacement batteries, and I can't remember the exact price he quoted me, but if I remember correctly, it seemed like he said that you can buy a replacement battery for a bit less than the retail price of ~$550 (maybe somewhere in the $400-$500 range?).
I'm not super happy with how my battery is degrading, however, I've gotten 2000 miles out of it and it's still working just fine, and given that the stated range on the 2015 IZIP E3 Dash was 25-35 miles, I think that as long as I'm getting at least 25 miles of range in the lowest pedal assist mode, my battery is working just fine and I don't really have good reason to complain.