I've checked the resistance on the Alternator wiring and it seems to be in the recommended range of about 0.22 to 0.34 ohms, however a) that's at 20 degrees (not about 13 as it is now) and b) my multimeter seems to be a bit screwed as when I directly touch the probes together it registers about 0.3 - 0.4 ohms instead of zero (and there's no zero adjustment!) but it only goes up to about 0.6 or 0.7 ohms which looks ok.
There doesn't seem to be any shorting to ground either.
The battery is a sealed gel-type so there's nothing I can do with that.
Taking the alternator apart requires tools I don't have and, from looking in the manual, is probably out of my comfort zone, so I think I'll have to take it to the garage
ADDENDUM - Ah, just seen Fazerider's post. When the bike's at home it's always on the Optimate, the battery was new only just over a month ago and I've only done about 800 miles since then, so I don't know if that would count as "prolonged undercharging".
There doesn't seem to be any shorting to ground either.
The battery is a sealed gel-type so there's nothing I can do with that.
Taking the alternator apart requires tools I don't have and, from looking in the manual, is probably out of my comfort zone, so I think I'll have to take it to the garage
ADDENDUM - Ah, just seen Fazerider's post. When the bike's at home it's always on the Optimate, the battery was new only just over a month ago and I've only done about 800 miles since then, so I don't know if that would count as "prolonged undercharging".