A list of the locations and quests where you can obtain gratitude crystals, and the rewards you can get from giving them to Batreaux, in The Legend of Zelda: Skyward Sword.

List of Individual Gratitude Crystals

Gratitude Crystals on Skyloft at Night

Sleep in a bed on Skyloft until night, then go outside to the following places to find these Gratitude Crystals.

1. Behind the tree in the northern part of the residential area of Skyloft.
2. Near the Bird Statue after you go through Waterfall Cave.
3. In the place where your Loftwing was trapped behind wooden boards (go through Waterfall Cave to get there).
4. On the lower level of the Light Tower.
5. On the lower level of the area north of the Bazaar, between two narrow wooden bridges.
6. On the ledge southwest of the Bazaar that you can reach by climbing down some vines.
7. In Orielle and Parrow's house, near the window and fireplace.
8. On the rafters inside of the Sparring Hall (use the Beetle to get it).
9. In a flowerpot next to the second floor door inside of the Knight Academy.
10. In your room in the Knight Academy.
11. (Requires the Clawshots) Go to the roof of the Knight Academy and use the Clawshots on the target inside of the chimney. Drop in and go through the crawlspace to reach Zelda's room. If it's daytime, sleep in a bed until night to make a Gratitude Crystal appear in her room.
12. (Requires the Clawshots) In the top of the waterfall on the large floating island above Waterfall Cave. Use the Clawshots on the vines on nearby floating islands to reach it.

Gratitude Crystals at the Pumpkin Landing at Night

Sleep in a bed in the Lumpy Pumpkin until night, then go outside to the following places to find these Gratitude Crystals.

1. Inside the Lumpy Pumpkin on a shelf on the second floor.
2. Outside in the pumpkin shed east of the Lumpy Pumpkin building

Gratitude Crystal on Beedle's Island at Night

On Skyloft, ring the bell on Beedle's Airshop, then go to the window inside of the Airshop and sleep on the bed there until night. Go outside and use the Beetle to get the Gratitude Crystal floating above one of the Airshop's propellers.

Gratitude Crystal Quests

The following quests can be completed to get 5 Gratitude Crystals each (except for "Rescue Orielle", where you can get five from Orielle and another five from Parrow.)

1. After Skyview Temple Find Kukiel
2. After Sleeping in a Bed Multiple Times Peatrice's Admirer
3. After Skyview Temple Rescue Orielle
4. After Getting the Gust Bellows Clean Pipit and Mallara's House
5. After Defeating the Imprisoned Deliver Cawlin's Letter
6. After Getting the Clawshots Find Bertie's Baby's Rattle
7. After Activating the Light Tower Find Dodoh's Party Wheel
8. After the Sandship Fledge's Strength Training (also awards a Piece of Heart)
9. After the Second Battle with the Imprisoned Find a Pumpkin Patch Plower for Kina
10. After the Second Battle with the Imprisoned Replace Sparrot's Crystal Ball
11. After the Second Battle with the Imprisoned Find Beedle's Horned Colossus Beetle
12. After Learning the Water Dragon's Song Retrieve a Rare Plant for Owlan

Gratitude Crystal Rewards from Batreaux

Batreaux will give you the following rewards for the Gratitude Crystals that you give him.