Battery case unusable

[SalvadorFreeman]

Hello, I got this tablet (PO22 version) and the battery case. The trouble is, the tablet uses the internal battery in priority, drawing almost nothing from the accessory battery, until it gets down to almost zero and turns off, even though the accessory battery is well charged, as shown on the dual battery percentage.
Is this a design fault, or am I missing something?
At the moment, the accessory adds weight but no extra battery power.

 

[Tim1954]

Is there no button to push to activate the charger function? I have two battery cases and they both need to be manually started...

 

[SalvadorFreeman]

No button on my case.
Where is your button?
Also, the notification shows the level of charge both in the tablet and the battery.

 

[Tim1954]

Ah ok. The Samsung backpack had button on top left corner. The other one has a chrome button down low on the back...