I have a Z20t-C-15M. SN 5H071828H. Online specs says there's a battery inside the docking keyboard and a battery inside the tablet.

Battery indicators is saying Battery # 1 is not present whereas battery led indicator in the keyboard dock displays no light (nor white nor orange).
Battery indicators is saying battery # 2 present and led indicator is white on the tablet.

Is this a normal behavior or an issue ? Why can'I get the secondary battery ?

From the specs :

Battery Life up to 9h30min tablet only (Mobile Markô 2014 running Win10)
up to 19h tablet & keyboard (Mobile Markô 2014 running Win10)