We stayed 4 days (5 nights) at Potsdam, a minimum 2 days for Potsdam except if you do not want to visit the interiors of the palaces (what would be a pity, esp. new palace) and 2 for Berlin.
This small (4 rooms, all on ground floor) bed&breakfast place with accessible garden lies ideally on a cul-de-sac giving direct access to the SansSoussi park. 500m from Charlottenhof train station to Berlin; 1,5km to city centre restaurants. In the room : 2 good beds, 2 chairs & table, TV, small bathroom shower-lavabo-wc). All perfectly clean and new. Breakfast cold buffet. Beer & wine sold at shop prices, thee & coffee free all day. Parking in the street. Friendly hosts (no English). €70/night.
Major + : location, quietness, no steps
Major - : no internet, and no free WIFI in town !
Info at pension-falck.de
foodtip : for excellent German food : Dreimädlerhaus, Elfbeinstrasse. 1,5km
A 2nd tip : Curry’s at ½ price for lunch next to the Jägertor 1,5km