1) A small difference between the left and right earbud battery is normal – the primary earbud handles the connection with the mobile and uses a little more power.

2) The earbuds switch primary/secondary roles automatically based on battery to balance usage.

3) Using one earbud more than the other (single earbud use) will also cause a difference.

4) If the difference is large every time, charge both earbuds fully in the closed case, RESET and reconnect. If it still persists then RPU.