Charge limit and battery bypass with the latest update by Google

 Google Pixel devices have added ‘bypass’ charging and 80% battery charge limit 

A few days ago Google rolled out the December Pixel Drop with a lengthy post about new Gemini features and more. What it didn’t mention is that Pixels now have an option to limit the battery charge, which caps it at 80% to extend its life. And there’s an extra feature too. This latest Pixel update seems to come with the side effect of being able to use “bypass” charging. The Google Pixel 8 series and the Pixel 9 series now support bypass “charging”, it powers the phone from an external source (typically a wall adapter, but a good enough power bank should also work) instead of the internal battery. To enable this, you need to toggle the 80% charge limit, then the battery will neither charge nor discharge once it reaches 80%.

The new ability for Pixel phones to limit charging to 80%, added with the December 2024 update to Android 15 QPR1, is designed to help protect the battery, as charging to full capacity has a bigger impact on the health of the battery over time. In a somewhat unexpected turn of events, another battery health-saving move in this update is the apparent addition of “bypass” charging. This new ability allows supported Pixel phones to stop charging the battery when it hits 80%, but continue to use power from a plug to power the phone. At least, that’s what seems to be happening based on tests. If you’ve installed the latest Pixel software, you will find the option in Settings > Battery. Toggle “Use charging optimization” and pick “Limit to 80%” (the other option is the familiar “Adaptive Charging”). This will enable both the charge limit and the bypass.

Using a power monitor, it was found that, after the battery had hit the 80% limit, the phone continued to draw power at a much lower rate which varied as the device was used for different tasks. When the phone was fully idle, it used 0.1W of power, but ramped up to 0.74W when the screen was turned on. When moving between apps, that moved up to 2.6W, and then hit 4.6W and 7.6W while using benchmarking apps. This strongly suggests that the device is simply pulling the power it needs at the time from the plug, rather than going through the battery at all. Turning “Adaptive Charging” back on immediately reverts back to power draws which align with typical battery charging behaviour. When power is used in this way, it saves a lot of degradation on the battery.

Major benefit would be when the phone is connected to the car. AA wireless is fine for short journeys but draws a lot of power from the phone. The downside is that it's always charging the phone, sometimes for hours after it's reached 100%. To verify that it worked, you can use an app to view the battery status, it should show the battery as “not charging” and the power source as “AC” (as in wall power rather than battery). Note that the phone will occasionally charge its battery to 100% and let it go down to 80%. All bypass features do this, it’s so that the circuitry can calibrate itself and give accurate battery charge level readings. The obvious benefit here would be in mobile gaming, as the device can get the power it needs without draining the battery, or overcharging it. This could also play a role in lessening heat generated by the device. That’s why many gaming-focused handsets directly support bypass charging modes. It is expected that bypass charging on Pixel devices likely won’t be used purposefully by many people, but it’s certainly a welcome option for those especially conscious of their phone’s battery health. And, as Google pushes for Pixel phones to be used for up to 7 years, this change could benefit battery health even if a user never knows it’s happening.

Now, since Google snuck this feature in, there’s no official word on charger requirements for bypass to work. The support page is quite terse and doesn’t mention any requirements. There are still a lot of questions here, primarily around what Pixel devices actually support this behaviour. The 80% limit is supported across multiple generations of Pixel devices, but this bypass behaviour has only been confirmed on a Pixel 8 Pro thus far. That does suggest it likely also works on Pixel 8, Pixel 8a, and the Pixel 9 series as well. Other brands have implemented a similar feature. Samsung, for example, calls it “Pause USB Power” and it does have requirements: a USB Power Delivery charger with PPS and at least a 25W rating.