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i have had my 03 for 5 years and have changed 2 alternators in 330000km that doesnt concern me but every year since iv owned this truck i have had to put a set of batteries in it it is always the passenger side battery that has a dead short in it and it is always closer to winter when i have to do it anybody have any ideas on what could be causing a dead short in one battery only
Luck of the draw. The batteries are in parallel and what one battery sees the other will also see. If they are lasting one year you should be getting free replacements. If not I would be looking att a diff. brand. Is the heat shield still on the passenger battery. If not it could be getting super heated from the IC tube. It get extremely warm, might even say hot. That could definitely do it.
Don't know what batteries you're using but the Motorcraft ones suck.
I had the same problem and every two years I had to replace my batteries. (03, 05,07, and 09) I used the motorcraft batteries because it's Ford and it has to be the best...not really. This last time I replaced them with Autozone Duralast Gold's, 1000 cranking and 850 cold cranking. My truck starts better, runs better, but only time will tell.