Battery drain on standby Idle

Hi Rajafromrawalpindi,

Thanks for your post and congratulations on your new iPhone 12 Pro Max! Based on what you've described, there is an issue with your battery draining more than expected while idle. We'll do our best to help out.

Disabling background activity is a great steps to test. When did you originally set up this new iPhone? Did you restore it from a backup? We ask because this may cause the issue you've been experiencing. As we restore from a backup, there are processes that occur resulting in slower performance and less battery life until that completes. The timeframe for this varies, depending on how much content needs to be restored. If that's the case, we'd suggest connecting it to a known good Wi-Fi network and charging it while this restore completes.

Note: When you charge the iPhone, we always recommend using an Apple branded cable and power adapter.

If that's not the case, make sure the apps are up to date: Update apps or use automatic downloads under section, "Update your apps manually".

Check for app usage under Settings > Battery and scroll down over the Last 24 Hours and Last 10 Days (if applicable). Look for any apps using more energy than expected. If you have an app that's using a lot, consider reinstalling the app: If an app unexpectedly quits, stops responding, or won’t open

Charge it up and test it out over the next 24-48 hours with any changes from the steps above. Should it persist, we'd recommend to Contact Apple Support

Hoping this helps out, cheers!