Alternator reserve capacity question

[Toecutter]

From the 03-05 Bin 'o Facts:

Alternator Output and Spare Capacity490 watts rated by Yamaha for '03-'05

120-130 watts spare capacity per Warchild before Datel drops to ~12.5 - 12.8v region

Is the spare capacity noted above in addition to running at full stock capacity? Specifically, with stock high beams on? Assuming they run concurrently with low beams (I can't check since I have HID headlights but seem to remember they do), that should put low plus high beam headlight power consumption at about 230 watts, right? (55x2=110 low + 60x2=120 high)
If all the above is true and my math is close, the 84 watts my HID headlights consume (after startup) should save me an additional 146 watts of headlight credit to add to the theoretical 120-130 reserve capacity for the stock alternator, for a total of 266 spare watts over a stock '04, using the conservative end (120) of the original spare capacity, no?

 

[Ignacio]

Assuming they run concurrently with low beams (I can't check since I have HID headlights but seem to remember they do)

They don't. Stock it's either high beams OR low beams...not both.

And I doubt it was scientific enough to split hairs on whether it's highs or lows that were on. Assume low beam as they're a few watts less than highs. No fan on obviously.