Chamberlain Liftmaster manufactures the Sears line of garage door openers and remotes. The Sears 315 garage door opener is part of the 315MHz security line of openers. The Sears 315 remote is the same as the Liftmaster 371M model remote. When the remote fails to operate the door opener, the first thing to check is the battery. Replacing the battery in a Sears 315 garage door opener requires a new lithium battery. Unlike other remotes, the battery in the 315MHz models uses a battery similar to a watch battery.
Insert a small flat-head screwdriver in the seam between the front and back cover of the remote control. Twist the handle of the screwdriver and pry the cover apart.
Pull the old battery out of the top cover. Insert a new battery with the positive side of the battery pointing to the top cover.
Place the two covers back together and press them with your fingers until they lock.