My Takamine electric-acoustic base has the battery in a compartment where the battery goes in contact-first and is held against the contacts by spring action and the compartment door. Very efficient and simple. And the whole thing has a footprint of less than 1/2 square inch. The panel with the built-in tuner and 3-band graphic equalizer and volume control is about 2x2 on the side of the guitar on the upper bout.