Ended up taking it back to the main dealer that did the warranty work incl. the 60ah battery replacement a few years back. After explaining the issue and asking if they had anything beefier "can you fit a Hilux battery in there?" they found a 65a Toyota battery (£85) and offered to fit and test the alternator gratis (all good), while I waited which was more convenient than doing it myself and having to book a slot at the local tip to dispose of the old one. Not 100% sure but it sounded as if the 65a is now standard replacement; so stock 40a, uprated to 60a, and now uprated to 65a.
My Covid usage sounds identical to @GravelRash but outcome more similar to @NJay 's last comment.
Trickle charge would be the obvious solution, but not practical where I live, so I've bought a solar panel to keep the power greedy little sh@t topped up when not in use. It's been making me nostalgic for my GT-Four - four months travelling, left on the drive, started first time.
Thanks for the help!
303 got a reaction from Test Drives Unlimited in Any reasonable solution to battery drain?