It is advisable to change batteries at a table or over a clean surface, at least until you get proficient.
The battery is located and held in place by a specially designed door. This is to be found at the bottom of the RIC or BTE style aid, and mounted in the face plate (the outer face) of a custom product. There will be a finger nail notch or a small raised area which allows you to open the battery door.
Depending on the make the battery will either remain in place when you open the door or will fall out readily. Note that the battery will have a positive and negative. The positive surface is flat and is the one with the sticker on when viewing a new battery. The negative surface has a step in it. When viewing a battery correctly placed in the battery door, you will note that it locates in a ridge that fits neatly round the step on the negative face. You must check the battery is correctly orientated in the door to avoid the possibility of damaging the body of the aid when closing the door, as well as to ensure the aid works correctly.