Battery advancements haven't kept in step with performance improvements, but the charging tech for topping those cells up has come a long way. Now, most phones come with some flavor of quick-charging technology that promises to fill our capacious flagships in arbitrarily small periods of time. But in the case of Google's Pixel 2 XL, it turns out that its "Charging rapidly" notification isn't always an accurate statement. In low temperatures, Google's flagship will claim to be charging quickly (10W+) when, in fact, it's actually charging at less than 4W.
The Pixel 2 XL charging at below ~20°C (68°F)
We were tipped off about the issue by a few of our readers, and though reports and our own tests only confirm this for the 2 XL, we don't know if the smaller Pixel 2 is also affected.
None of us here at AP had ever personally experienced the problem, but that is due to the circumstances required to trigger it. Turns out, if the Pixel 2 XL's battery temp is below about 20°C (68°F), instead of pulling the maximum charging speed (18W then falling to 10.5W), it will only pull 3-4W. Most confusingly, even though it's charging at sub-optimal speeds, the phone will actually claim to be "Charging rapidly," which is a bit misleading.
Of course, we had to try to confirm this behavior ourselves. We wouldn't be the Android Police if we didn't check and compare our results with other phones (and go a tiny bit overboard). If you don't want to read about the testing methodology I used, feel free to jump down to the results section.
Our own testing
"That Robin is clearly expired," -David
My analysis wasn't strictly the most scientific. I wasn't able to ensure that every phone was charged at precisely the same temperature, each warmed up at different rates, and my sample size was limited. But, I was able to reproduce the reported behavior on our Pixel 2 XL, and I did my best to test the other phones I had on hand with a similar methodology for comparison purposes.
In all, we looked at cold (sub-16°C/61°F) and room temp (24°C/75°F) charging behavior, as measured by my Satechi USB-C Power Meter with the following phones:
- Pixel 2 XL
- 2016 Pixel XL
- OnePlus 5T
- Essential PH-1
- Nextbit Robin
All phones tested were put in the fridge until their internal battery temperature reported around 16°C/61°F degrees, at which point they were each plugged into the meter fed by the Pixel 2 XL USB-C PD 18W charger. Values were recorded, the phones were then disconnected and left to warm up until the internal battery temperatures reported above room temperature (24°C/75°F) values, at which point they were plugged in again and values again recorded.
As much as I'd have liked to have the screen on to display reported battery temperature for better photos, the potential variance in charging speed with the screen on wasn't acceptable.
The trends from these results should be generally reproducible, but the conditions of the test weren't precisely lab-controlled, so YMMV. For example, I made sure all the phones were below a 50% charge, but they weren't all charging from exactly the same baseline in both tests, and numbers reported by the meter can vary a bit as the devices negotiate different power levels.
Note that these numbers are peak rates. In some cases, these values were not immediately reached or dropped over time.
In all, most of the phones tested suffered a small drop in peak charging rates at colder temperatures, excluding the Nextbit Robin. By far the phone to see the largest change, though, was the Pixel 2 XL, with a difference of over 12W.
Keep in mind, our testing methodology does leave a bit more accuracy to be desired. The sequential nature of the testing (i.e., from cold to warm the batteries did charge a tiny bit due to being plugged in for testing) and the effect of temperature on the battery itself (most devices reported varying levels of charge, less at cold temperatures and more at warmer) mean you can probably ignore the 3-4W difference seen by most of the phones. For example, I noticed that the OnePlus 5T showed a major drop in reported charge at colder temps that returned once it had warmed up, and below 60°F/15.5°C the reported battery temp was just incorrect.
This video wasn't part of the above testing, but it demonstrates the issue.
Even if we accept a 3-4W margin of error for changes in reported charge affecting charging rates, the Pixel 2 XL stands apart from the pack in a distinctly negative way. For whatever reason, the phone charges significantly slower at lower temperatures. Worse, it doesn't inform you of this, continuing to show a "Charging rapidly" indicator, even when it's only charging at ~4W.
Once we verified that the charging speed on the Pixel 2 XL was being misreported below certain temperatures, we reached out to Google for comment. Google confirmed with us that it's working on/investigating a fix for the UI, which we hope affects the "Charging rapidly" language that appears on the Pixel 2's lockscreen. So, hopefully, as part of a future update, your phone won't tell you it's charging quickly even when it's actually not.
- Christopher Aliapoulios and Kai Markeli