I finally managed to find the solution:
1) Battery was old, I changed it to new one and puff, no longer error message about missing hw.
2) As said, in Power Board Prefs I couldn't change year bigger that 2003, however in Workbench's own Prefs there ain't similar restriction. Small miracle happened and I found manual for KCS Power PC Board, which stated following about manual usage of pcclock -utility:
By typing 'PCCLOCK OPT SAVE' you relay the tima and date to the hardware clock on the KCS POWER PC BOARD. From now on the hardware clock will always have the correct time and date, even after switching off the AMIGA. By typing 'PCCLOCK' after switching on the AMIGA, you can read the time and date of the hardware clock on KCS POWER PC BOARD. Therefore it is logical to incorporate the line 'PCCLOCK' to the start up sequence on your start up disk.