I just bought a refurbished iPhone 8 with 256 Gb.. Everything looks fine... except that the battery drains really quickly. If I charge it up to 80-85% and then leave it on the table, without using it (screen turned off, obviously), the battery will have drained in less than 24 hours.

This is with IOS 15.2 installed but without any apps except the stock ones; in fact, without even a SIM card or iCloud configured, just with Wifi connected to the local network.

When I connect it to the Mac to check it using coconutBattery, it says that the refurbished battery is fine:

Battery state

14 cycles, 389 days, "Desay Corporation" (which is what my original iPhone 8's battery also says, so it must be the same part that Apple uses)...

Is there any reason why I shouldn't return it? Is there any obscure reason why a new battery might give trouble during the first cycles, or why IOS 15.2 drains battery much faster while idle...? Anything other than the obvious explanation that it's defective?

  • There could be a number of things happening to drain the battery, apart from it just being defective. A good way to start trouble shooting is to look at the battery settings in the iOS device which will show which apps consume the most battery. Another way to trouble shoot is to see if the issue occurs in Low Power Mode or when Cellular Network & WiFi are disabled. If the device was just set up it might be doing a number of tasks in the background such as indexing Spotlight and syncing with iCloud or other services that are set up. Jan 1, 2022 at 17:11
  • There are no apps working on the background. I was testing the phone's battery, so all I did was turning it on and leaving it on the table.
    – PaulJ
    Jan 1, 2022 at 18:47

1 Answer 1


If you are sure the replacement battery is good, and you don't have a lot of background tasks running on your phone (apps that can access the internet even when not open), I can confidently say that the culprit is ios 15+.

One of it's new features is to detect unauthorized non-Apple parts on your device. On newer iPhones (11 and above) if you go to Settings > General > About, there will be a new section called "Parts and Service History". This will highlight if your battery, display or camera (depending on the iPhone model) is "Genuine Apple Part" or not.

Another new feature in it is Optimized Battery Charging (Settings > Battery > Battery Health > Optimized Battery Charging) that determines how and when your phone battery should be charged.

If Optimized Battery Charging is enabled, your phone may or may not charge fully depending on what Apple's algorithm decides (overall, I find it a useless feature more designed to collect our personal data - you have to enable location service to allow Apple to determine the places where you spend a lot of time, and also allow Apple access to data on how you use your phone).

On older iPhone models, I believe both the above mentioned features are quite buggy (to be cynical, deliberately buggy to force us to buy "Genuine Apple Part" or upgrade to a newer model).

I am confident about this because I too have the same problem on an iPhone SE (1st generation) on which I replaced a battery from another iPhone SE. It worked fine, without any issue on the older ios 9 until it was upgraded to ios 15. After the upgrade, it doesn't show the battery charge correctly at all, and keeps shutting down abruptly.

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