Uneven battery drainage of AirPods 4 ANC

Here’s what’s happening:

- If I leave the earbuds in the case for 1-6 hours at 100% charge, they lose over 10% charge within 10 minutes of use (sometimes one earbud, sometimes both). It seems like they don’t hold 100% charge for long after being taken out of the case.

- However, when I open the case after such a long period, the iPhone screen shows both earbuds at 100% with the lightning bolt (as if they just finished charging).

- On the other hand, if I start using them shortly after charging (5-20 minutes), they hold 100% for about 20-25 minutes before draining.

- Overall, they last over 4 hours without ANC but with speech recognition and spatial audio enabled. When they don’t drain immediately, they last 20-30 minutes longer, which feels significant.

- After extended use, there’s a 5-12% difference in charge between the earbuds—is that normal?

**What I’ve tried so far:**

- Reset the earbuds to factory settings multiple times.

- Reset my iPhone to factory settings.

- Disabled Find My for the earbuds.

- Updated iOS from 18.2.1 to 18.3.

- Fully drained the earbuds and case to 0% (though the case showed 1% and made sounds with the indicator light on).

- Waiting for a firmware update (current firmware: 7B20).

I already returned one pair, but the replacement has the same issue. The store’s diagnostics found no problems, so I’m wondering if this is just how they’re designed or if there’s a fix I’m missing.

**Details:**

- iOS 18.3

- AirPods firmware: 7B20

- Assembled in Vietnam

Here's the translation:

From today's observations: I found out that one of the earbuds (or both) can drain by 10% or more when left in the case in standby mode for several hours—like after sleeping, for example. However, when I charge the earbuds through the case and use them shortly after charging, they work fine. My earbuds were assembled in Vietnam on 11/05/2024.