Here is a video I found which is very detailed and shows how to add a second battery to your bike:
Video: How To Add 2nd Battery to the Fiido D2
Here's the link to the battery which was recommended a ways down in the comments section:
36V 10Ah Battery Supplier
In the video he explains that you are adding the second battery in parallel. Thus both ...
IMO if you get a schematic drawing for the bike you should be able to purchase a 2nd battery and find a method to connect that battery in parallel to the original.
Having a second battery in parallel would mean both would charge & discharge at the same time. This should increase the life of both as heat from charging/discharging is a major ...
Yes in theory but the gain is not practical. You’re better off swapping batteries than trying to jury rig something.
Let’s do the calculations.
You note that the AC charger puts out 36VDC at 2 amps. That’s 72 watts per hour.
Even a modest eBike has an 8Ah battery, for a total of 36x8 or 288 watt-hours.
At 72 watt-hours per hour charging it takes four ...
Copenhagen Wheel can be built up with most common rim types, and it appears you don't need a cassette because it has internal gears. Ive seen these around my town and they seem quite practical. https://www.superpedestrian.com/en/tech?_ga=2.58737453.1683893135.1584469426-223915906.1584469426