Jim - thanks for sharing this info. I also bought a blank key and found that they do indeed unlock any Rad bike battery!!!!
I also thought about using a U lock on my bike, I just have to find one that will fit my 2019 RadCity ST.
I am in Seattle and when I find a lock or some other method of securing the battery I am going to visit the RadPower showroom and show them the key and ask them to consider selling some sort of battery locking device.

Along with some attachment for towing a trailer!