[Elecraft] KX3 Battery Questions

[Pete Meier]

If you have batteries installed and then plug in an external power supply to the KX3, which source is actually powering the KX3?  

I noticed that, in the above situation, batteries installed and external power source connected, that if I lowered the external power source voltage, the KH3 remained at the battery voltage level. So it appears that the batteries took over.

This makes me wonder if that external power source voltage is "touching" the batteries. 
Can someone tell if I need to remove the batteries when I plug in the external power source?
I  don't want to apply that external power supply voltage to my battery pack!

Pete WK8S