Thanks for contacting us about your EVELO Electric Bicycle - we want to make sure you get the best reliability and life out of your bike!
It's a very good idea to make sure to charge the battery if is is in storage for more than 2-3 months, during which time it should be kept in a temperature controlled environment.
One thing I recommend is getting a timer that you can plug the charger into. You should get one that can be set to charge the battery once a week for an hour or so.
I'd recommend this timer from Amazon for about $15: Westek TE06WHB 2 Outlet Digital Timer with 2 Grounded Outlet, White
This will handle two bike chargers at the same time.
Let me know if there's anything else I can do to be of assistance. I'm here to help.