Audi A1, A2, A3, A4, A5, A6, A7, A8 remote key, fob not working, repair, battery replacement

My car is Audi A6 C6 BPP 2005, but it could be the same issue on A3,A4,A7,A8 etc.
So about my problem:
Sometimes when I tried to unlock the car the fob did nothing. Led light on remote flashes, but there was no response from the car.
Some other time it opened central locking system when I came close to car - similar like in keyless go system (which I do not have).
Sometimes the only way how I could unlock the car was with physically putting the key in doorlock and manually unlocking. However, sometimes I was unable to start the car.
At some moment all the problems disappeared and all was working as it should. But then again problems re-appeared.
I thought the fob may have been somehow broken, so I tried operating with the spare key. Unfortunately, the exact same problems started. Batteries had been replaced in both of them.
I scanned the car with VCDS and there were no errors from any of the modules.
I did the coding and tried a lot of other options what I could find in forums.
One morning the battery in my car was fully drained out, so I bought and replaced it with a new battery. But it didn’t solve the issue.
I dissasembled the fob and found out that in both keys the microswitches weren’t working properly. The reason of that was the acid alkali leaking from the batteries..
As you may see in this video - cleanig procedure is what eventually solved my problem.