Red interior battery light went on @ noon. Later that night all the lights went dim, all electrical went out and stopped running. Bought new alternator from NAPA, they recharged batt. for a while. I installed everything, it worked great for 4 days. Then the exact same thing happened. I swapped batteries with a 03 F150 to get me home. Even with the newer F150 Bat. my inside bat. gage was below normal telling me that the alt was probably shot again. When I got home I noticed my original battery was low on water. About 36 oz's. Would this low water in the battery cause the alt. to go out? Someone mentioned it may be a regulator problem between the starter and the alternator. Suggestions would be apprerciated.