Well, as I expected, the dealership found no problems with the battery OR the charging system. They also said their tests showed no "parasitic battery draw". I guess that means they found no short-circuit using up the battery. I thought it HAD to be one or the other, but those folks always know SOME way to explain problems away non-professionals won't think of.
I don't drive enough! They swear! They say I do only local errands and that I'm just NOT driving it often enough. I sure hadn't expected THAT as a cause, but they MAY be right. Its a 2005 car and I've only driven it 23,300 miles. And fewer than 2,000 miles/year the last few years.
Basically, (they say) I am draining the battery through starting it several times in short errands and not driving it long enough to recharge the battery. They suggested several ways to prevent similar future problems (several of them idiotic from my point of view).
1. I could just drive the car to nowhere and back twice a week for at least 15 minutes.
2. I could leave the car idling in the driveway 15 minutes twice a week.
3. I could drive longer routes to my errands.
Do those also seem idiotic to you?
4. They suggest I slap on a battery charger in "trickle mode". That means recharging the battery after the usual short multi-stop errand trips and giving the battery a slow auto-shut-off charging. But that means that twice a week, I need to find the hood opening lever in the car, prop the hood up, attach the charger to the battery, and then undo all that each time I want to use the car. For the life of the car (which, quite frankly, I expect to last 20 years at the rate I use it).
Doesn't THAT seem a bit idiotic to you also?
What I NEED is a plug-in car. Oh wait, that's called a hybrid. And I expect that is what I really need. An electric usage for the usual very local errand-shopping where I can just plug it in each time after use; and a gas engine for the longer 2 hour trips to family events and or towing the boat on 1 hour fishing trips.
Lifestyle choices do cause some specific demands. But (and mine are admittedly not the routine car-usage demands), one has to adapt equipment to them. I love my Toyota Highlander, but it WILL be 10 years old next year. And I've read that the Highlander Hybrid will be redesigned and improved next year. It may be time to replace it then. I can deal with a weekly routine of keeping the battery charged up properly for a year I guess. Not happily, but I'll consider it something like getting routine haircuts, brushing teeth, cleaning house, etc, until then.
But I'm still ticked off about the entire situation...
AND: To 'Sometimes Cats Herd You', thanks for the url to the neat gadget that cuts off battery drain. It COULD have solved me problem if there was a short (apparently, not the problem). I'm going to get it anyway "just in case" that solves the problem. I'm also looking for some battery charger I can just plug into the cigarette lighter to make trickle charging easier as a backup.