Other than the distributor "maybe" being the cause of falling RPM at idle, there can be no connection between a problem in the dist as you describe, and the charging system. Treat them as two problems, fix one or the other and then attack the problem that is left
As usual, you beat me to it. My first thought was that it was two separate problems. I'd treat the charging system first, since a dead battery can leave you stranded in a bad place at a bad time.