Racing Spoon

Sure, exactly. As you say, it's very easy just to use a trickle charger inside your own garage- so a small solar panel would solve every other situation apart from very niche cases such as long term airport parking.

The dashboard ones the AA sell aren't very big, or do they not work? I was thinking the same surface area across a longer thinner panel should at least help.

Seems very odd to me that Lexus don't just bung a small solar panel somewhere in the top of the windscreen or rear window and avoid the flat battery issues entirely.