Sidewall generators are noisy. Even if they do not slow you down much, you will think they are slowing you down. Not sure if that many miles would destroy the tire from rubbing on the sidewall generatr or not. In other words a dynohub is likely the solution if you do not do the big battery thing.
Sum of:
Hub - $80 or more.
New spokes for wheel - $30 or more.
If you do not buy a new rim for it but instead rob your old rim off your current wheel - $0.
Wheel build charge at bike shop - $<I have no clue what that costs, I build my own wheels>
USB charger - $40 or more.
Likely need a pass through cache battery - ??? (the ones I use are no longer sold, I do not know what a good one would cost).
Or, buy a couple power banks that cost a lot less. Run your phone with minimal backlighting, screen off most of the time, any apps not needed turned off, airplane mode to minimize power use, etc.