"I bought this together with the Train Bridge and Tracks (10872) and the engine with an empty car can't make it to the top of the bridge 30%-40% of the time. When using the app, the motor is noticeably weaker and stops 90% of the time before reaching the bridges's top. The tracks+bridge were setup on a flat, solid surface. Fresh AAA Energizer batteries were used.
This is just nitpicking on an otherwise amazing set."