WARNING: This page is about a different car, the 2009 Acura MDX, 2008 Acura MDX, and 2007 Acura MDX. However, it is still accessible from the selected car via links, so may be relevant.
Remove the cover (A) from the remote control.
Fig 1: Identifying Cover From Remote Control
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Remove the batteries (B).
Replacement Battery: BR3032
Confirm that each operation works normally after replacing the batteries.