Why my airpods only charge 80% right earbud but left earbud and case charge 100%?

Hi phornthipha,

You started from a great resource: If your AirPods won’t charge - Apple Support

For help with charging your AirPods, ensure the case and connections are clean. The steps below found in the article here can help. How to clean your AirPods, AirPods Pro, AirPods Max, and EarPods - Apple Support

"Clean your AirPods and AirPods Pro

• Don’t run AirPods or AirPods Pro under water.
• Use a soft, dry, lint-free cloth.
• If your AirPods or AirPods Pro are exposed to anything that might cause stains or other damage—for example, soaps, shampoos, conditioners, lotions, perfumes, solvents, detergent, acids or acidic foods, insect repellent, sunscreen, oil, or hair dye:
  • Wipe them clean with a cloth slightly dampened with fresh water and dry with a soft, dry, lint-free cloth.
  • Allow them to completely dry before placing in the charging case.
  • Don't attempt to use them until they're completely dry.
• Make sure not to get any liquid in the openings.
• Clean the microphone and speaker meshes with a dry cotton swab.
• Don't use sharp objects or abrasive materials to clean your AirPods or AirPods Pro.

Clean the case of your AirPods or AirPods Pro

Clean the charging case with a soft, dry, lint-free cloth. If necessary, you can slightly dampen the cloth with isopropyl alcohol. Allow the charging case to dry. Make sure not to get any liquid in the charging ports. Here are a few more guidelines:

• Remove any debris from the Lightning connector with a clean, dry, soft-bristled brush.
• Don't use abrasive materials to clean the charging case.
• To avoid damaging the metal contacts, don't put anything in the charging ports."

You can also find helpful information here: Charge your AirPods and learn about battery life - Apple Support

If the issue remains reset your AirPods and test charging again. How to reset your AirPods and AirPods Pro

Cheers.

Try turning off "Optimized Battery Charging" in the AirPod's settings while they are connected. It does wonky things to the battery levels between the 2 AirPods. I have turned it back on since doesn't cause much for issues for me. Maybe it will add a little more life to the AirPods in the long term.