Ford Super Duty (1999-2016) :: 2005 F350 - Truck Seemed Slow To Turn Over / Battery Dead

I bought a 2005 F350 in January of 2012. At the time of purchase, I noticed that the truck seemed slow to turn over. I talked the dealer into installing 2 new 750 CCA Ford batteries at the time of sale.

I have put less than 7,000 miles on the truck since the day I bought it. In August of 2012, I went to start the truck and the batteries were completely dead. I charged them, started the truck, and the next day the truck was dead again.

I took the batteries out, and took them to the dealer. They replaced both of them under warranty. They said that after they charged them, each tested at less than 85 CCA.

In July of 2013, the same thing happened. I used the truck one day, and then the next day the batteries were completely dead. I had them tested at the dealer, and the passenger side battery failed the test. The driver's side passed. They replaced the passenger side under warranty, again. This time, they also cleaned all battery / ground connections and tested the charging system. Everything passed.

Last week, I went to start the truck. Same thing again. Took the truck to the dealer, and both batteries, after charging, failed the test. They replaced both batteries under warranty.This time, on each battery, the dealer had written with yellow paint pen on the batteries AND on the radiator shroud "BATTERY NOT UNDER WARRANTY."

I asked the dealer about this, and they said that since they have replaced 5 batteries in the truck, and since it has 152,000 miles on it, the warranty is no longer valid. I argued that since they have checked the truck thoroughly, and found no issues with the charging system, they can't void the warranty like that.

So, what is the reason why the batteries would fail like that, and that frequently?