Battery with a dead cell - yes, I agree, a strong possibility. Easy to do a load test / cell check at any auto store. I have had headaches before with the directional switch. It is like the brain box of the wiring sometimes. Many problems can be traced back to a bad directional control switch.
If you are taking your voltage readings directly from the battery, it's definitely not your switch! Bad battery or charging system issue, as others suggested.
