The buttons often stop working because the contracts get dirty. If you're tech savvy you can open the shell by twisting it and then clean the contacts. First remove the batteries. Then grasp the end of the shell with the on and off buttons in one hand and grasp the lower end with the zero button in the other. Slowly apply torque like you are ringing out a rag. You will have to twist fairly hard. Soon you will hear a clicking/cracking sound and the case will begin to come apart along the seem between the front and back parts of the shell. Once an edge begins to open you can carefully pry the sides apart slightly.

As the shell opens, a few of the parts inside will be free to move around so, go slowly and keep track of the position of all the parts. I used alcohol to clean the contact surfaces.

I've had my remote for about 8 years and have cleaned the contacts about every two years when a button stop working.   After cleaning, the remote works like new.