Can anyone identify this rtc cmos battery conector please?
Can't say for certain - will update answer if measurements come in. But, this JST-2(PH) looks pretty similar. Mates with this.

I'd further support this guess by saying that JST-2(PH) is a really common battery (especially li-ion) connector, but before you go buying 10 reels, keep in mind this is just an assumption from visual inspection.

EDIT: Considering that connector is 2.00mm, definitely not it. However, does 1.25mm sound like it's within margin of human error? This Molex connector has the same detent profile