2003 Excursion, 7.3 diesel. New batteries three years ago, replaced them under warranty 4 months ago, picked up two new ones again yesterday. Batteries had leakage on top. Don't want to read or search through all threads for an answer. Would appreciate any advice or help.

 

Good Morning !
Hope when you state leakage you mean liquid leakage, because if batteries are allowed to stay wet on top the wetness will provide a path for the battery to drain itself of any charge if left alone long enough. Sooooo,
Usually, when there is an overcharge condition present, it will cause the batteries to "Cook" until dry and the level of the electrolyte drops low enough inside the battery and the plates inside get distorted and cannot function as they should.Then the battery will eventually fail.

Overcharge condition can be caused by a malfunctioning charging system or a poor connection involving the charging system, where the system does not send the correct info and the alternator thinks the battery(s) are low and increases the charging rate and cooks the battery(s). Before replacing anything, the system needs to be checked for good grounds to start with.

 

Check the Fuse box?

 

You can if you want to.
If the system was not charging at all, I would suggest checking the fuses.
I am going by the info you provided and the leakage is what I paid the most attention to. If the "Leakage" is coming from inside the batteries There could be a problem with the batteries or usually an overcharge condition will cause electrolyte to spew all over the top of the battery..