Thanks VSKID3 and Cobb. Sorry to be so slow in responding. Don't mean to be rude but granddads get pretty booked up when the weather gets nice here in the Northwest.
@VSKID3: No, our driving habits haven't changed and we don't/haven't noticed anything different other than the fuel mileage.
@Cobb: "...using a grid charger at 350 ma to float the cells helps it along..." What is a grid charger? Is there something I could look at that would explain it and show how to use it with the Highlander? Can I find out which cell is bad/weak and replace just that one(s)? Also, what is an "Enginer PHEV"? Sounds like something I should look into.