Review this article for info on battery life, charging your Pixel 4 / 4 XL and what type of charger to use.
Battery Specifications
Pixel 4:
Up to approx. 25 hours of Usage Time when Always on Display (AOD) is off
Up to approx. 9.5 days Standby Time (AOD Off)
2800 mAh Li-Ion non-removable battery
Pixel 4XL:
Up to approx. 32 hours of Usage Time (AOD On)
Up to approx. 12 days Standby Time (AOD On)
3700 mAh Li-Ion non-removable battery
Battery Basics
Battery life depends on the network, signal strength, temperature, features and accessories used.
It's common for batteries to be warm from use or charging.
Don't use a charger that hasn't been approved by the manufacturer as this may damage the phone.
The Pixel 4 / 4 XL has a Type-C charging port which allows for more data throughput and can support technologies such as Adaptive Fast Charging.