The MCT-3 has been replaced by the MTS3. See: https://www.pssstore.net/products/linear-mts3-visor-transmitter-3-channel

I couldn't say for certain why your remote is going through many batteries. As far as the number of buttons, quite typically, home owners that have multiple garage doors and/or vehicular driveway gates will get remotes with multiple buttons so they can designate a specific button to a specific garage door or gate.

Here is the manual, it shows you how to replace the battery. https://cdn.shopify.com/s/files/1/1666/9427/files/pdf_MTS3_manual_b0d77696-7243-4ec3-a281-f32ee9444e51.pdf?v=1699127103%20