If you want to focus on aerodynamics, you could start with an aero front fender, just cut up a panel and attach it to the forks and curve it up to the front fender. The more you cover, the more winds will affect you however.
Here is what my CBR 250R's stock fender looks like compared to an aero fender for the older CBR 250 Four.
On the bike. It took a lot more work than I thought it would!
I haven't run the fender on my CBR enough to confirm the difference is noticeable, and won't be able to confirm until it comes back from painting. I had it on for one whole tank, and that was my best tank yet, but it just squeaked above my previous record and I was tucking on highways with very little romping for that whole tank.
I would take a guess that the tires on your bike right now are bias ply with tubes. You can seal up spoked rims to run tubeless, but you shouldn't do that without tubeless tires. I believe there was a rim profile change around the 80s, so not all rims are tubeless compatible, even non spoked rims. Finding a radial tire in an old bike size is usually pretty difficult, but worth a shot.
Running a dying battery can lead to other much more expensive electrical problems later on, continue at your own risk.