In Belgium and the Netherland there are companies who tried this and some where suc6full, major problem is the BMS
as when removing or changing the setup of the batts is produces some errors, don't know how to solve.
https://www.fietsaccu-revisie.nl/ebike-accu-reviseren-per-batterij/stromer
Maybe a little late but good for someone else.
https://www.elektrofahrrad24.de/spezial-ersatzteile-stromer#.VgbjoP2hcxt
https://www.stromerebike.com/collections/spare-parts
I stripped the E3 to strictly nothing printed some 3D parts and build it in.
A new reflector was needed as I unmounted the original light with build in reflector.
I'm happy with the result and much brighter.
I didn't remove my wheel as I put the nut on the inside. used the same holes as the Stromer bracket (left side) and made/welded a
custom coupling in stainless steel
Look at the inside of the fender and you will see how it works, better visible at the front fender.
In this weather maybe you have to clean the inner part to see.
2 nothes to free. I got it of for my homemade rear light integrated in the upper part.
Last week I had a flat rear and patched while wheel was mounted.
If you don't have to change the tube or tire it is the quickest way.
15 minutes and done.
It took me some time to produce the connection between the ST2 and the trailer
but today the first testride to see if all fits.
Some minor things to do: Better Stromer fitted ss bolts and plastidip them in black.