I actually got the GT380 out today - and ended up pushing it home

Had major electrical problems, with things beginning to 'shut down' and the bike started missing a lot. Switched the lights off, and things improved for a while as I limped homewards. Then the indicators stopped working, and the dimly glowing neutral light extinguished itself about a mile from home.
Closer inspection and removal of the battery revealed no electrolyte in the cells, which might not have been helping things

Now on charge - fingers crossed - and further investigations pending.