Hey there prashanth_p,
Thanks for reaching out to the Apple Support Communities. We understand you're experiencing issues with your iPhone battery and mobile network after updating the iOS on your iPhone. We'd be happy to look closer into what's going on.
To get started, when you say that the network is restarting unexpectedly, are you seeing "No Service" or "Searching" as described in the 'Related Article' that was shared along with this thread? If so, have you gone through all the steps provided in that resource, including contacting your carrier to check for any issues on their end?
If so, then we would recommend reaching out to Apple Support directly using the 'contact Apple Support' link listed under the "Get more help" section. They'll be the best option to look into this issue further.
As for the issue you're experiencing with the battery life, give the steps listed in the following resource under the "How to maximize battery performance" section a try: iPhone Battery and Performance - Apple Support
We hope this is able to help.
Take care!