[prairieschooner]

What is a desulphation routine?
Where is the best place/price for new batteries that you have found?

The Equalizing Phase of the Power Inverter will perform the Desulphation. Basically the Lead Plates collect a Corrosion Layer that is referred to as Sulfate and if removed extends the life of the Battery. Letting the Batteries get Discharged by non-use would not produce this although I suggested it as a way to maybe extend their life, same process as 77 suggested.
I priced Batteries and warranties and decided on NAPA because they are usually close by to where we travel. I choose a Flooded Lead Acid for the Engine Bank because my Charging System is set up for them. I typically replace them every few years because they are relatively inexpensive for what they do. This type of Battery is designed to typically last 5-7 years although some claim extended life with other devices like the Power Pulse (I bought one but disconnected it because I don't like anything connected when I leave the Coach).

As a side note I attended a seminar on batteries that was put on by Interstate Batteries. He stated that a Flooded Lead Acid Battery can Freeze! and when any Load is put on a Frozen Battery it CAN EXPLODE! I actually had this happen one year and expect that it was from freezing. He did state that AGM Batteries do not suffer from this. 77 was very lucky.