I am impressed by your solution and I took have at least one bad leg. I have decided against batteries in favour of a basic bike that I can park anywhere and carry up stairs. I want the little and often mobility with a few longer rides over summer. I also have a neighbour in his late seventies that rides 'naturally aspirated' with a buddy that is two years older. His buddy has an ebike and he is giving it a couple of years before he goes electric.
Being younger than him, I feel that I need to stick with 'naturally aspirated'.
I am interested in going the other way to get a dynamo with that switchable between lighting and USB power, for my phone and speakers. There is 3A at 6V to play with.
Ultimately I would want mild hybrid, with regen so all assistance is pedal powered.
I'm 60+ it was either the e-bike, wreck my leg even further or take the car. That was an easy choice :)
Be careful with what you've got... I wish every day that I could do the day I messed up my leg again without making that particular mistake. I rode a low racer recumbent at speed and had a nasty case of leg suck when hitting a (new to me) speedbump.