Nice! I actually have 6 of those automatic air wicks all around the house. Cool little DIY you got there.
I noticed that, once your battery is low, the motor will become weak which will still depress the air scent nozzle, but enough to just barely spray any out. I threw in 2 rechargeable 2500mAH batteries, and what a big difference in the power of the motor depressing the nozzle. Its shoots 4 feet long mist.
Would that be a problem as the battery gets low? I'm assuming you did run it on the standard battery setup.