Members of Source London who have paid the £100 annual fee are now able to use any of the points.
Earlier this year, mayor Boris Johnson announced plans to install 1,300 charging points by 2013, scaling back from the 7,500 he promised a year earlier.
But the Green Party said the mayor's electric car ambitions had "gone flat".
Source London is a network of charging points across London which can be accessed by plug-in electric car users who have registered.
'Air quality benefits'
Green Party London Assembly member Darren Johnson said: "The mayor never explained how he would fund the ambitious plans for 25,000 charging points which he launched with a big fanfare in 2009.
"He has also failed to guarantee that the charging points will run on renewable energy, so the environmental gains are far less than they should be."
Kulveer Ranger, from the mayor's office, said: "The mayor has been leading the national charge on electric vehicles having championed them in London for the past three years since his election.
"There are obvious and immediate air quality benefits to the increased use of electric vehicles, helping us to deliver an improved quality of life for Londoners."
There are currently 2,100 plug-in electric cars registered as exempt from the congestion charge, according to the mayor's office.
