Look at the illustration to below.
Note that the battery slides under the aluminum “bridge”, “clip” or “bracket”. Do not place it on top. Please be sure the plus (+) side is up. Incorrect insertion will burn out the circuit or break the solder connection.
The cover should only be finger tight (snug) so as to remain waterproof. Please, do not use pliers or a pipe wrench, as over tightening will damage the O-ring