2008 F350 Super Duty batteries and alternators keep dying. Why???

How long since a tune-up? Any applicable trouble codes?
Are you saying it went into limp home mode, not much power, or you lost all electricals and it died?
If it is the latter, make sure battery has a full charge and battery connections all good. Check your charging system. Follow one of the positive battery cables, see if it goes to junction block, if so, check fusible links.
Any electrical component that doesn't work, if fuse protected, check that fuse circuit for voltage. Some fuses are hot all the time, some go hot with the key on. Use a test lite.

Someone would need to check the circuits to find the short to ground or a component that is using power.
We usually start with the alternator and check the major components first.

maybe the wrong size battery is in and maybe a fuse or wire problem

you can disconnect the negative battery clamp for 5 minutes to clear the CEL, but if there is something wrong it will eventually come back-the best thing to do is have the OBDII connector scanned (free at most commercial auto parts stores) and report back with the actual code for more thorough help.

Hello there
FORD TRUCK
Wheel Nut Torque Specifications
Make/Model Description Years Torque Make/Model Description Years Torque
FORD (continued)
FORD TRUCK
E250 Van 8 Lug, 9/16" 2008-88 140 -160 ft lbs
E350 Van 8 Lug, 9/16" 2008-88 140 -160 ft lbs
Escape - 2003-01 98
Excursion - 2003-01 160
Excursion - 2000 148
Expedition - 2003-01 150
Expedition 19mm Hex 2000 100
Expedition 21mm Hex 2000 150
Expedition - 1999-97 100
F Super Duty Pickup 10 Lug, 9/16" 2003-99 165
F Super Duty Pickup 10 Lug, 9/16" 1998-96 140
F150 Pickup - 2003-01 150
F150 Pickup 19mm Hex 2000 100
F150 Pickup 21mm Hex 2000 150
F150 Pickup - 1999-88 100
F250, F350 Pickup 8 Lug, 9/16" 2003-01 160
F250, F350 Pickup 8 Lug, 9/16" 2000-99 148
F250, F350 Pickup 8 Lug, 9/16" 1998-88 140
Ranger, Windstar - 2003-87 100

One thing that I would check is the connector that plugs into the alternator. I have seen these connectors go bad and not allow the alternator to charge. Check for battery voltage at the post on the back of the alternator too

Try taking the + positive battery cable off for about 5 mins then replace it see if it'll reset it.

disconnect negative battery terminal and isolate from battery, remove serpentine belt remove mounting bolts and wiring connectors remove alternator
you may need to gently pry the alternator loose from the mount

Must be a broken wire or a bad connection from your alternator.

Slot 24