Can the boards be used when battery runs out?

Yes. You will ride like a regular skateboard. Push forward by your feet.

Is the Electric Skateboard Waterproof?

All of the enSkate boards meet with a IP54 waterproof standard - Not advise to ride in rainy day, and please keep it dry all the time, take care of it when you don't use it.

How to adjust steering sensitivity?

You can use a T wrench to adjust the tightness.