Bikes died ?☹

[Dudeofrude]

So went out for a ride earlier and all was going well but as I pulled up at a petrol station I noticed the bike sounded a little rough. Didn't think much to it and put it down to the fact I've got a new chain and 'silent' sprockets so have been hearing more random noises than usual due to the quoter drive train.
Anyway it started to sound worse and everytime I can to a stop it started to sound more and more 'chuggy' sort of like a twin? But this was only on idle. It would fluctuate between 800-900 to 1200-1300rpm and be really rough. Also started back firing like a twat on every over run or gear change.

Managed to get back to my house and literally as I pulled up outside and put the bike into neutral it cut out, engine light came on and wouldn't restart! Now if I try to start it the whole system goes off and restarts (like the battery has suddenly failed) and just kicks up an error code 46.
I've checked and that indicates an error with the 'vehicle system power supply'

So what do we think the issue is? I've never known a battery to fail like that? Not to affect the engine running etc and certainly not while running?
So am I going to be looking at something more substantial? Something like a rectifier maybe?