When you arrive late at BER Airport you are literally lost when you prefer to use public transport. Using a taxi from the airport to the city is very expensive.
I consider a late arrival a flight that is put on-block at 22:15 or later.
Today the situation was worse. Two train platforms were closed. This resulted in adjusted train connections. Getting to Gesundbrunnen left you with a S-Train connection to BER Terminal 5 to catch the rerouted FEX train. The FEX connection takes about thirty minutes, when the rail network works as expected. Using the S-Train connection take approximately fifty minutes. Even though it is still a better connection compared to taking the bus to Rudow and the underground U7.
The bad thing about making the right public transport choice is that there was no information about the train changes at BER Terminal 1. The connection display was empty.
When you travel to BER Airport I highly recommend the use of the DB Navigator app on your mobile phone. Check the available connection while still on board of the aircraft prior to disembarking. Another app you should have installed and configured is the BVG app. Buy your ABC ticket while on board. This helps you to stay calm while trying to find the right platform for your select led train to Berlin.
There are two BVG apps available, BVG Ticket and BVG Fahrinfo (Connection Info). The first does not provide timetables but supports you buying tickets easily.