Cycle analyst is a cool thing. If you wanna know what's going on electrically, they tell the story.
Had mine for little less than a year, shoulda got one sooner. I find that monitoring the wattage, the voltage drop and comparing that to speed and road conditions helps you develop a good "feel" for what 400 watts will do, the difference between 600 and 700, etc. Highly recommended if you can afford it.