Garage door still can open and close in a power outage

albertkao wrote:There was a power outage in my neighborhood.
All the lights in the garage and my whole house cannot be turned on.
When I pressed the garage door opener button on the garage wall, the garage door opened.
I drove my car outside.
I closed my garage door by pressing the remote of the garage door opener in my car.
Why the Chamberlain double garage door opener still had power to open and close?
i.e. I did not need to open and close the double garage door manually.