trying to determine when a battery is going to fail is like playing the lottery. the location you live it has a great affect on a batteries health. just like said above, you do not want to replace just one. if one goes Tango Uniform then replace both of them at the same time. Down here in the hot dry heat, batteries (cheaper ones) don't seem to last as long. Up north were I am from the severe cold winters take their toll on them as well.

 

i had a 96 powerstroke...i changed the factory motorcrafts in 2005 because i was nervous....they were still starting the truck just fine...even at 15 degrees up in the mountains.

New batteries showed no improvement in starting at all

dual batteries seem to last very well...at LEAST 6 years

just make sure you replace them in a set...

 

My batteries in my 05 were changed back in April. Went to a baseball game, came out and it wouldn't start. Looking back I did notice that it was starting slower.

Aaron

 

I still have the factory batteries, and they recently tested fine. As they are only $90 ea from the dealer, I can't imagine going to another battery which would cost more and probably fail sooner.

 

one of the reasons i eliminated my heater grid as well...i felt like it is undue stress on the batteries and the alternator since it never gets below 15*f here in the winter