The battery's manufacture date.

 field  octets  contents                  range
 =====  ======  =======                  =====
   1      1-2   year                      0..65536
   2       3    month                     1..12
   3       4    day                       1..31
   4       5    hour                      0..23
   5       6    minute                    0..59
   6       7    second                    0..60
                (use 60 for leap-second)

This field will be set to year = 0 if the agent cannot provide
the module date.  The hour, minute, and second field will be set
to zero (0) if they are not relevant.  The year field is set
with the most significant octet first.

The string will be empty if the battery does support
this function.