A quick follow up on this thread - I had to replace the original Banner battery on my 2017 Plus 4 and suffered the EML coming on and the fuel gauge not working (showed empty, with the orange warning light on).
Following Roger's experience I tried the "disconnect-for-half-an-hour" method and it worked, much to my delight. I just removed the negative lead, didn't bother with any fuse removal/reseating, as that would have involved more work removing the parcel shelf and tool tray.
