How I know if my iPhone is hacked?

Battery draining is no indication that your phone has been hacked. You will find the battery draining quicker when you have Social Media apps that you have allowed background processing. Also if your Battery Health has dropped below 80%, you will find unpredictable battery performance. You can run Safety Check to make sure no one else is signed into your account and to review the information you are sending to others.

How Safety Check on iPhone works to keep you safe - Apple Support

It's VERY VERY VERY difficult to impossible to hack an iPhone. If your battery drained, go to Settings > Battery and look at what used the most power and make adjustments as necessary.

A non-jailbroken phone cannot be hacked. what do mean that your phone was “drained”?