Apple Watch Series 4 battery dies quick
I charge my watch over night, however the battery runs out mid day
Apple Watch Series 4, watchOS 7
To understand Apple Watch performance and its relation to your battery, see:
Apple Watch Battery and Performance - Apple Support
“Battery life” is the amount of time your device runs before it needs to be recharged. “Battery lifespan” is the amount of time your battery lasts until it needs to be replaced. Maximize both and you’ll get the most out of your Apple devices, no matter which ones you own. See the "Tips for Apple Watch" section in:
Batteries - Maximizing Performance - Apple
If the battery drains too fast after an update, see all the replies to:
Update 6.2.1 Battery Draining Too Quickly… - Apple Community
Battery Drain since watchos 7.4 - Apple Community
FWIW, in some cases, unpairing the watch, completely erasing it, then pairing and restoring the backup will resolve the battery draining issue after an update. Also, some people have found that simply waiting a few days after an update resolves the battery draining problem.