Alright, something I have encountered and know the answer.
I started adding and adding and ended up with dead battery after two days to and from work.
I had changed the headlight to a 80/100w xenon bulb, (from stock 55/80) and a changed tail light from 35W to 45W bulb. Then I added two 35W running lights. And then when I would run it all going and from work, I would only be up to speed about 10 minutes. Ran all at high output twice and had dead battery. Oops. Thought it was battery. Recharged and had same thing happen again. Then looked at output of stator/battery and draw from all the lights and the starter and lights were pulling more than the stator could compensate for. So I run running lights, and low head light, and put the bike to a smart charger and no problems.
One of the columnists from Motorcyclist mag said that this is a common problem as the engineers only plan for minimal add on electrical and when you try to add more, the battery can't handle the drain, and the stator puts out less than the draw, so it is in a negative state most of the time.
And he said even the big bikes are the same. They don't plan for you adding grip and vest heaters, big/bright light bars, etc..
Of course the longer you ride to and from before stopping, the more of a chance that you will output enough current to charge battery. Look at the comments about the horn add-ons, and how they dim the lights when they are engaged.
Oh well, one of the limitations.
It's still a fun bike to ride.
Bill 8)