I need help with my tablet. When I connect the keyboard (with battery) power led start blinking

4 amber and 1 white

When I use tablet without keyboard everything if fine.

The tablet see the keyboard battery but uses only main battery. The keyboard battery wont discharge and it is not in use. 

I checked the batteries in Dell Command power managment. Both batteries are excellent health.

Then I disassembled both keyboard and tablet. The batteries are different form-factor but the connectors are the same and the voltage is almost the same (0.2V)

So I swaped them vise versa. And the situation is the same. 

It does not matter, which battery is installed in the keyboard. I cant make the pc use the secondary battery.

Where is the problem and how to make it work?