Anyone can help me?

You normally have to use the battery that came with the computer. There are no replacement or upgrade batteries yet available at Dell--the only source to use. There is a choice of batteries when ordering according to this review:

https://www.reddit.com/r/Dell/comments/c0hwoh/early_review_of_dell_inspiron_15_7000_7590/

Batteries should come from Dell to be sure of authenticity. Dell computers must have genuine Dell batteries. Here's what comes up when searching Dell-

https://www.dell.com/en-us/shop/pfydresults/258959?categoryId=2999

We are just users here like you. Dell replacement batteries must be used and they must come from Dell. That is an old post you cite and if you read it you'll see those batteries were not available even back then. The 9570 model is not the same as your 7590. Batteries are not cheap, usually over $100. 

Thanks for your answer.

I know that there is a choice when you buy the notebook, but if you want the 97 Wh battery you have to choose the i5 version, or the i7 with 4K display. I need the i7 version with the FHD display, but this comes with 56 Wh battery.

https://www.dell.com/community/XPS/XPS-15-9570-not-recognizing-XPS-15-9550-battery/td-p/7260929

In this post I see that these four batteries are compatible with the XPS 15:

GPM03 97WHR, 6 cell
5XJ28 97WHR, 6 cell

5D91C 56WHR, 3 cell
CP6DF 56WHR, 3 cell

Are the same for the Inspiron 7590?

I only would like to know what model of battery is compatible with the inspiron 7590 and where one can buy them, since they aren't avaible on the dell online store.

Does anyone know the answer?

Hi i was wondering if you had any news about switching the big battery in place of the small one?

Sorry to tell you, the 97wh battery cannot replace the 56wh battery. Because it's longer than a 56wh battery. But 56wh battery can replace the 97wh battery. 

You can refer to the picture below.

Can you tell me your original battery Type? I'll try to find it for you.

@JAC8513 Hi, but I see some space there around the hard drive bay, so is there any possibility that you can just put the new battery, but lose the space of the hard drive bay

It depends what HDD you are using since there are 2 SSD slots. Mine came with SSD so I was able to upgrade to the larger battery with no issues.