Servo Motor, External Power - Battery

I have seen projects connecting Servo Motors externally on 4x AAA batteries.

But I did not find one connecting to 2x 18650 batteries, why ?

In the image, could I change the Servo Motors power for 2x 18650 batteries without problems?

The servo motors are: TowerPro SG90 Mini Gear Micro Servo 9g For RC Airplane Helicopter Sale - Banggood USA

And the 18650 batteries are: BAK B18650CA Cell Specifications | Second Life Storage & Solar

image: http://prntscr.com/mmo7ab

SG90 servos are specified to work on 4.8 to 6V.

2 x 18650 batteries are 7.2V nominal, 8.4V fully charged. That's a lot more than intended. I wouldn't risk it if I wanted the servos to be reliable or long-lasting.

Steve