iPhone turns of at 50%

Apple can replace a battery in 30 minutes or less, but there may be a backlog of repairs ahead of you. Usually they can finish it in a few hours, or worst case the next day.

And usually they don’t erase the phone, but you should make a backup ahead of the repair in case something goes wrong.

Here is more information→Get your Apple device ready for service - Apple Support

What is your battery health at?

Batteries degrade over time with usage due to chemical aging, that's just how they work.

You can expect about a 1% drop per month with average use on an iPhone.

Apple recommends replacing it when it reaches 80%. To check your battery health, go to Settings > Battery > Battery Health.

iPhone Battery Replacement.

iPhone Battery Repair & Replacement - Apple Support

About Lithium Ion Batteries

iPhone Battery and Performance - Apple Support (IN)

There's the issue. Apple recommends replacing the battery when the health reaches 80%, you're at 71%, I'm surprised the phone powers up at all.

Replace the battery and your problem will be solved.

iPhone Battery Repair & Replacement - Apple Support

Yes, just take it to an Apple store or Apple certified repair center, have them replace the battery and your problem will be solved. Click on the link below, then click on the Get Service button, then click on the Find a Location button and go from there.

iPhone Battery Repair & Replacement - Apple Support

You’ll find that it will get much worse, quickly.

First it’ll start dying when you’re on a call …

… then you’ll not be able to make a call w/o being plugged-in.

Then it just won’t work at all.

We can’t emphasize enough how quickly this “final slide into total failure” occurs.

Make arrangements w/ Apple NOW to get it repaired at a time of your choosing; or you’ll find yourself “phoneless” … often when you need it the most.

Val_rey wrote:

How can I prevent my battery to not go down so fast and keep it healthy ??

Your battery is past its useful life. It is dying. It cannot be fixed. There is nothing you can do other than replace it.

Using Apple’s Battery Service Online site, we’ve always “booked” a specific time to bring our phones in to a store for a battery replacement.

Longest wait was maybe 2 Hrs; at a VERY busy store.

Unsure if this same reservation capability is available, and as always, YMMV.

Not to any place, it must be either Apple or Authorized Apple Service center. You can view cost and set up appointment here. That will solve your problem.

iPhone Battery Repair & Replacement - Apple Support

YES make an appointment.

That way they’ll have the parts needed.

Those are ”textbook” symptoms of a worn-out battery.

Follow Kurtosis12’s advice, and you’ll likely be astounded at the improvement in your “old” phone’s performance.

It’s almost like getting a new phone again.

I have like 5 months with it and it was new

Very unlikely since the iPhone 12 was discontinued 2 years ago. It's more likely that someone told you the phone was "new", and it wasn't.

But, let's assume that it really was new. That being the case, the phone sat in a warehouse somewhere for 2 years before you bought it. That would have been about the worst thing that could happen as far as the health for the battery.

Do I need to make an appointment to go change my battery or I can just go ?

Make an appointment if you will be taking the phone to the Apple Store.

You won't need an appointment if you take the phone to another authorized Apple Service shop. Most of them keep spare batteries on hand....but there are no guarantees.

You can find authorized service shops using this link: Find Locations

Val_rey wrote:

It’s cause I am shocked because I have like 5 months with it and it was new

It can’t possibly be new. That model was discontinued 2 years ago. You were scammed by whoever you bought it from. Return it.

Expect a battery to last about 2-3 years before it will need to be replaced again.

Batteries decline. That's normal. Nothing you can do to avoid that.

Re: “… how can I prevent the Battery capacity to go down … “

See this article for some “best practices”:

Batteries - Maximizing Performance - Apple