S8977SHV 2K is 22V version of S8931.
12V servo benefits Using low amperage and less stress:
1) Extends servo life
2) Extends battery usage time
3) Ability to keep steady torque while flying
4) Industrial friendly
Specs Operation voltage: 12.6V
Torque: 638oz-in 46kg-cm
Speed: 0.09sec/60 deg
Weight: 2.68 oz / 76g
Dimension: 1.57 x 0.79 x 1.59 in / 40 x 20 x 45 mm
The firmware in a 2k servo verifies the position of the servo arm two thousand times each second, while the firmware found in previous servos verify the arm's position one thousand times per second.This greater number of verifications makes for a very precise servo, and gives it a more "solid" feel.
It is recommended to use a booster cable with 2k servos to ensure steady voltage at all times.