I need a bit of help please.

Its an MC21 With a TYGA 300 motor (the Campsa Honda that was on the home page once)

I recently got home from a trip to Scotland (1000 miles in 3 days). On the last leg the bike ran but I lost all lights. All except some glimmers in the warning lights.
Optmate brings the battery back fine but it quickly returns to nothing when out with the headlight on.The bike actually runs fine though.
Before I get too involved with the spanners, (I don't know what I'm looking for) is there a simple check with a meter that may pinpoint the fault.
I'm hoping just a replacement regulator will do it but electrics baffle me.
If thats the case has anyone got a spare on a shelf?

Thanks for reading this, Mal.
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