Can anyone tell me if the positive terminal on the Varta battery is of a substantial girth?
Reason for the oddball request is that I can't tightenten the positive clamp on mine, not matter what I do it's always loose, which obviously causes problems.
I've just looked at the battery, and the positive terminal is slightly smaller in diameter than the negative.

Forgot to add, it's not a Varta battery on my motor

Asian motors often have a smaller + terminal, is this a new battery if so it has the wrong post size.

Yep, less than a year old

I've got 4 newish Varta batteries and all of them have the same posts. The positive posts are all larger diameter than the negative posts by about 3mm. If your clamp isn't tightening you can either widen the clamp so that it sits further down the post before tightening it, pack the clamp out by inserting a piece of lead or flattened copper pipe and tightening or buy a new clamp.

Buy a new clamp for a Japanese import.

Getting me hands in a Varta battery to see if it has a bigger post, if not, it's a new clamp.