2001 7.3 has a hard time starting after sitting for more than a day. When I first turn the key on, I noticed the voltage meternal drops to about 10v but then slowly rises. When I crank it over, it drops to the red line, about 8v and cranks extremely slowly. When it finally turns over, it chugs hard for about 5 seconds. Volt meter then returns to about 12-14. I disconnected both batteries completely from one another ad tested voltage. One tested at 11.96 and the other was 12.83. Both negative terminals had a significant amount of corrosion build up for whatever reason. Any ideas?