As devices age it is expected that some problems may arise. Smartphones are not built to last years and years. They now almost always include an internal non user replaceable battery. This has shortened the life span of many phones as the phone is useless once the battery expires which normally takes about a year and a half. Some phones begin to experience lag as the memory in the phone ages. These issues are to be expected. The Nexus 6P is about a year old and is still one of the best devices around. I would happily carry the 6P as a daily driver. The 6P continues to hold its own against more powerful and newer flagship devices.
The current bug effecting Nexus 6P devices is causing phones to shut down before the battery is completely expired. Some users are reporting that their phones shutdown at 15% while others are reporting that their phone shut down at 60%. It's easy to sympathize with the frustrations these users are experiencing with their devices shutting down at random with now power left. I saw this myself on my rooted Nexus 6P my phone would shut down at 15% and I could not turn on the phone until it had been on the charger long enough to bring it well past 15%. The only fix was to return the device to stock and then re-root with the updated SuperSU file. The issue seems to be affecting users who are not rooted as well. The bug has been submitted to the AOSP Issue Tracker and this particular bug has been starred by 1200 users. This seems to be a real issue. Hopefully Google can get this bug squashed quickly.
via XDA