power outage

I live in a hurricane and thunderstorm prone area of the country. I have external power banks, I keep charged to be able to charge my phone with if the power goes out for an extended period of time. Many such devices can be found on sites like Amazon.

Here is a link for some you might want to consider --> https://www.amazon.com/s?k=power+bank+for+iphone+15&crid=3T38IB4VCW2VW&sprefix=power+bank+for+iphone+15%2Caps%2C123&ref=nb_sb_noss_1

Car charger.

I shall assume you mean “charging” your iPhone 15 and not “powering on” since all iPhones have internal batteries that last a long time when fully charged.

Of course when you have a power outage your plugin charger block will not work until the power is restored. You would have to have a generator or battery power station to charge your iPhone.

So not really clear what you mean by your question.

The built in battery.