Just got a volt-meter in the mail today for the cycle. It was only $5 through Electric Vehicles, USA.
Electric Vehicles USA, Inc
Yep, it's analog and doesn't have any actual volt markings on it. It's perfect!
Just throw it into the tachometer housing and I can finally check my state of charge at a glance.
(Yes, I still have a digital multi-meter for testing and troubleshooting, but I wanted something I could bolt to the cycle and leave there!)