In the meantime the OBD2 ‘memory saver’ arrived from Amazon so it was out with the spanners.
And once the air filter had been removed, I could see two 7mm bolts holding the mounting flange for that big pesky rubber tube with the ‘immovable’ clamps. Released those, the air box opted out and the battery slid forward to give access to the terminal clamps.
Less than 45 mins from start to finish and the job is done.
