If your battery is fully charged, but you have no power, I would first check the connection to the battery. Is the wiring to the battery tightly fastened and in contact with the battery terminals?
Does the battery have a build-up, rust, dirt or corrosion on the battery terminals where the wiring harness connects to the battery? A layer can build up on the terminals of the battery, wiring harness ends or both over time, especially if the battery is outdoors or in moisture.
To remedy this, take a wire brush and clean both the battery terminals and wiring harness ends, reconnect tightly and give it another shot.
If the terminals are covered with a white crumbly sulfur type material, good chance this is the issue.
Another thing to check is whether a fuse has blown on the wiring harness or in the object it is operating?
If everything checks out, your battery has probably put on some age and ran its course (RIP).