Handlebar E-Bike Key Storage Slot

My wife got an Rad Power Cycles Radcity e-bike, with a key lock for the battery. Unfortunately she can't ride with the key left in the battery, as placement is such that it will interfere with her leg. I don't want the key to get lost, and needed a way to keep it with the bike when the key is not in use (and the bike is not secured).

I have created this handlebar mounted storage slot, for the key to reside while she is riding the bike, etc. The slot is just the right size for her key that