As widely reported, Google’s Android 9 Pie update to their Pixel phones killed battery life on the phones. This affects both Pixel and Pixel 2 phones.
A typical scenario is the phone loses up to 50% of its battery capacity in 5-8 hours, even when the phone is hardly used at all.
I found that if I turn off Wi-Fi, then battery life is back to normal. That is, in the same scenario, the battery has lost just 7% of its capacity with 93% battery capacity remaining.
Google was made aware of the problem at least by the end of August as shown on their Issue Tracker, but no word yet on any fix to this serious Android defect.