The YS640 uses .75 amp of power at startup, 2.25 amp of power during ignition and then .50 amp thereafter. The big power hog is the igniter. Fortunately, you can manually ignite your smoker and bypass the igniter altogether. That would be the "least power way". Those igniters tend to be a bit finicky, so, I'd certainly recommend the manual process. Here are instructions for that:
1. Remove the cooking grates, heat diffuser & the burn grate.
2. Reach into the hopper cavity on the left side of the igniter tube and pull the igniter wires into the firebox.
3. Unplug the igniters weather tight connection and then push the wires back into the hopper cavity.
4. Reinstall the burn grate & place a small handful of pellets onto the grate.
5. Light the pellets with a torch, starter gel or starter stick.
6. Once lit, turn the power switch to the on position and allow the fan to run across the fire.
7. If the flame continues to develop press the start button and reassemble the grill.