On Tue, 8 May 2018 17:59:38 +0100, Graeme
wrote:
snip

I think a new battery is the answer, but I'm really only guessing. I'm
no electrician (auto or otherwise), and apart from some logic and basic
testing, I just don't know.

Given that the battery requirements of a MM are pretty small, do you
have a similarly sized battery in another vehicle that you could swap
for a week or so?

Assuming it has a cranking handle, even *another* older battery might
do, or if you don't need to start it, even a motorbike battery would
provide information for your 'is the battery self discharging' test?

Have you mentioned how old the battery is yet (in case I missed it).

Cheers, T i m