I installed a device known as Priority Start on my '02 Explorer and another on my '07 Expedition because the battery on either could be dead in a couple of weeks of just sitting. As noted this is SOP.

My daughter has the Explorer parked outdoors at college and Priority Start gets her going even after many days on non use. My Expedition went into that mode last weekend for some reason, maybe the rear glass was open (?), I never found out.

Let us know how the EverStart works out. Is it a sealed or cap-type battery?

-- Chuck