@linmob yeah DB has the tendency to do traffic shapping and drop your connection speed if you download more than 100 (or maybe 150) MB of data.
Besides that some areas in Saxony it's not easy to use the train's internet.
Going south from Saxony to Bayern is even worse.
@joao I was using my own 4G connection, but.. Brandenburg is apparently not great in terms of 4G coverage, at least not with O2 :D