306 GTI Starter Problem

I was on the road with my car today, the problem of the car is not starting.
This morning, when I went to work from my house in Üsküdar, the battery light was on while I was driving. I was in a hurry to go to work as soon as possible because of working hours and bridge traffic, as I worked in the resignation.
I set off in the evening and the indicators on the Bosphorus Bridge flashed. At 2000-3000 rpm, the battery light went out, but when I stopped in traffic, at low rpm, the battery light came on again.

I came to Üsküdar in the evening. There was flickering in the headlights and extinguishing in the right headlight. the car trembled and stopped at the pistachio tree. When I turned the key, it just didn't work. we took them to my house in sultantep with friends.
either there is a problem with the battery or it is not charging.
At the authorized service (peugeot altunizadede) the battery had changed and it was 2 months or so. And the cable of the sound system was not attached, I brought it back and tied it. I think there might be a leak in the connection.

What kind of trouble can there be in the vehicle? did they install the exhausted battery or is there a charger or other problem? It seems strange to me that the battery light goes out at high speed and turns on at low speed.

And now lies in front of my house where can I take it tomorrow Saturday?

thanks in advance.
Good evening