The mBot IR remote is designed to use a CR2025 3-volt coin cell battery.
We have also used a CR2032 in that remote. The last two digits in the battery code is the thickness of the battery in tenths of a millimeter, so that slightly thicker battery can work. It is the same diameter, 20 millimeters, which is indicated by the first two digits of the code.
For completeness: the C stands for Lithium and the R stands for “Round”.
FYI, the same CR2025 coin cell is used in the Hand-Grip Heart Rate Monitor.