Heated grips intermittently not working?

'24 SP, add ons: Clearwater Darlas, Ducati heated grips, Warm & Safe heated jacket. Total pull w/ all at max = 178 watt / 13.7 amps. Stator output = 490W / 35A. With lights at 3/4 and jacket at 1/2 the heated grips won't work on high...low is ok but cuts off at a stop when rpm's drop for a minute or so. After up to speed again, grips go green and are working again on low. On high and medium the grip icon goes black and they stop heating. Turn light as low as they go, and the jacket off...then the grips work on high. Duc shop here says that they do not know how much the bike itself draws (fuel pump, etc), so if they do not know that, I don't really trust them to figure this out. Plus Duc will likely refuse warranty due to non OEM add ons.
So the questions are: Anyone know what the bike itself draws, ie: is it possible that the bike itself draws 300W or so, thus I'm maxing out the output? Bad battery? Bad rectifier? Things to check? Best guesses?
Thx in advance as intermittent electrical gremlins are not my strong suit.