The Mogawak Shrine in The Legend of Zelda: Tears of the Kingdom can be found in eastern Hyrule at Zora’s Domain under the walkways in the water.
Enter the shrine to begin The Power of Water challenge. Head down the stairs. Once at the bottom there will be an elevator straight ahead that leads up to the altar. Grab the battery on the ground in front of it using Ultrahand then bring it up the ramp and place it on the pedestal.
Along the wall you’ll see a cylinder with a board stuck to the side. Under it there will be an additional board. Stick that board on the opposite side of the one already on the cylinder.
You’ll then need to turn the whole thing so that one of the boards is in the water. This will cause it to spin, powering up the battery. While here, use Ultrahand to drag out the chest in the water. Inside this chest you’ll find a Magic Scepter!
Grab the charged battery then head down the ramp and go straight across to the other side to find another pedestal. Place the battery on the ground next to this pedestal. Activate your Ultrahand and drag the balls in the water as close as you can to each other in the middle of the pool. Next, place the battery on the pedestal to electrify the water and power the gate on the other side.
Jump in and quickly make your way across the electrified water to reach the chest containing an Opal. After making your way back across the water, bring the battery back to the other side and place it on the pedestal to charge it up again. Once charged, take the battery up the stairs next to the elevator.
Hop in the elevator then place the battery on the pedestal. This will power the elevator, allowing you to reach the altar where you’ll receive a Light of Blessing.