E36 clock setting

Guys im having a mare with the e36 18 button obc clock.

Battery died a while back so the clock was reset to blank. Iv been trying to set the time/date for a while with no avail.
Iv read the owners manual and online sources and they all say the following

When the display says 'input time' use the 1,10,100 and 1000 buttons to get the correct time showing then press the set/reset button and then do the same process to set the date.

Problem is, I use the 1,10,100 and 1000 buttons to show the correct time no problem there but when I press the set/reset button its doesn't save it, infact it clears it back to blank again! Iv also tried holding the set/reset button for a while to only get the same result.

Anybody ever experience the same?

I remember having this exact same issue with my old e36 m3 and I eventually got it but I cant for the life of me remember.

Every time I get into the car the obc flashes 'input time'. this sort of anal stuff bugs the hell out of me!