[ree]

Nope. I've had one more mysterious dead battery since May, but that's it. It's so spurious that I've just decided that I'll live with the deep cycle battery + jumper.

If it's happening regularly for you, take it in. If it's no longer under warranty, you're concerned about the cost of diagnosing it, and you have some educated guess about what system might be the culprit, it might be worth investing in an ammeter. Wire it into your + terminal hookups and note the discharge rates at periodic intervals times while the vehicle is off. I'll look in my manuals for in-spec current's to expect (no promises I'll find the numbers). Then if you seem something larger than those, start pulling fuses in the systems you think might be to blame until the current measured by the ammeter drops to expected levels.