Does it improve battery life

Which update are you referring to? 

1. iOS Update? Which Version? Update your iPhone, iPad, or iPod touch - Apple Support
2. Carrier Update? Contact Carrier. Update your carrier settings on your iPhone or iPad - Apple Support
3. App Update? Which App? Contact App Developer? How to contact an app developer - Apple Support
4. Apple News Update? --> Read the latest headlines in the Apple News app - Apple ...

The measure of battery health deterioration/drainage is subjective and can vary depending on individual usage patterns and not iOS version updates. There is no universal standard to determine whether the battery health deterioration/drainage is normal or abnormal because it heavily relies on how the battery is used and maintained.

Protect & Prolong the Life of your iPhone's Battery:

1. About the battery usage on your iPhone, iPad, and iPod touch ...
2. Batteries - Maximising Performance - Apple (IN)
3. iPhone Battery and Performance