That unit will only display the battery indicator/picture. The "battery power setting" is only to set the voltage of your battery, at 100% charge, so the battery indicator will be more accurate. There are 5 levels so, 28v for a 24v battery, 42v for a 36v battery, 54 for a 48v battery, 58v for a 52v battery, and not sure about the last one. Maybe 80v for 72v battery. Anyhow, you'll want to select "42" since the Roadster comes with a 36v battery. That display doesn't have a way to show the remaining voltage, only the picture of the battery level.
The PAS Ratio Parameter Setting is what drew me to this company. I have a 700 series bike. A nice touch. When I was looking at all the different ebikes, I found some that were reported to have intense "giddyup" at PAS 1. I like to have options and get the bike to my liking, even though I didn't know what even was before I had a bike. During my first ride, I had no issue with the default settings. I took pictures of all the settings before I started to play with them. If you find any PAS level too intense or too weak, you can change each level to your liking. I did find out that setting any level to 100% will give you the max controller output. In your case, 36v battery at 15 amps will produce 540 watts. Unless you can change the default Current Limit Value Setting from 15a to 18a. The manual says that you can change it to 18, but the manufacturers firmware may be different. That would grant you access to 648 watts.