@Philbert 

I will talk tomorrow with my friend about the hardware needed and to see what he replies 

Will keep you updated tomorrow!

Thanks!

EDIT

  @btx There was someone else doing the IT/cabling there, and he did a shitty job. They overpaid, old hardware, messy, and not happy in general. They didn't want to bother me in the beginning because we are friends. Because of many problems, they asked me to fix a few of them. I went to one of their apartments, and they had the EAP115 on their wall, but the internet was very slow and unstable and she could see shared folders of other people and other people could see her pictures that she (accidentally shared on the network without a password) When I put the cable in the 115, it wouldn't go over 50mb via the cable and it would go around 60-70 wireless. When I opened it, I could see there was a POE injector behind the wall. When I use that cable directly, it goes ~519mb. The POE injector is using just a regular power socket between the walls. The cables they have are between 120-200 meters, measured with a cable tester. Theoretically, I can cut around 10 meters from the cable since they kept a spare 15 meters, but I dont want to burn my fingers on that. 

They have their equipment in the basement with an AC. If the switch makes noise, is not that bad. It might disturb the cars that are parked there ;) 

EDIT

  @ArjanKS 

Hey

The cables they have are between 120-200 meters

This bit is a concern for you if that is the length of runs, hopefully, this is CAT6 cable?  Look for marking on it that state 23 AWG as that will mean its full copper cable, if it says CCA its copper coated aluminium which isn't good..  hope its AWG

Cat 5/6 is designed to be run less than 100m, once you pass that threshold performance degrades exponentially which is a concern.  More so if you are going to be running POE over this, that might explain the injectors and the placing of them.  

Thinking out loud here, it would make more sense to just have a POE switch centrally pushing the power down the run, however, if the cable is too long it may have affected the POE performance and therefore the previous installers had to place injectors at the device side.  From experience, this happens pretty quickly after 100m and the common issue is the POE device either wont power up, or trips out and restarts randomly, neither of which is good.   Usually putting an injector at the device end is the fix for this, but it's far from ideal as it indicates you are running cable lengths out of specification

A test for this would be to try powering one of your existing APs from the injector at the full run length..   You may find injectors to be better than POE switches on long runs.  Switches try to negotiate the power demand of the device, a long cable will affect this.. injectors on the other hand will just chuck out power regardless and this is an advantage in this scenario.

EDIT

  @btx 

Totally agree mate..   CCA is a disaster waiting to happen but sadly I have seen it before!  Contractor comes in 10% cheaper cause he is using what appears to be copper coloured cable, its alu core and runs fine for a slow network.   Few years down the line however its not worth scrap value and he's long gone.. CCA is good up to 50meters max and should only really be a temporary solution, hopefully its not the case and he does find AWG

Get the impression the OP was looking to keep costs down as much as possible so using the existing Injectors and cable may be the best option here.  Ideally fibre would be the way to go but its gonna cost a bit and require new runs

The joys!!

EDIT

  @ArjanKS 

Let me go through the comments. Unfortunately, my kids got covid, and a day after my wife. I am still going strong, but sleeping whenever I have time.