If the Northern Line Extension (NLE) is built, there will be six stops from Battersea Power Station to the City (Bank Station).  This should take about 15 minutes including the change at Kennington (NLE will be on the Charing Cross Branch).  In an experiment for the Oval Partnership, our resident blogger, yours truly, cycled from Battersea Dogs Home to the City (just over London Bridge).  It took 16 minutes obeying the Highway code (stopping at red lights!).  Once the time taken to walk to and from the station and waiting for trains is taken into account it is likely that cyling would be much faster.