  We show that the 3D charged Banados-Teitelboim-Zanelli (BTZ) black hole
solution interpolates between two different 2D AdS spacetimes: a near-extremal,
near-horizon AdS_2 geometry with constant dilaton and U(1) field and an
asymptotic AdS_2 geometry with a linear dilaton. Thus, the charged BTZ black
hole can be considered as interpolating between the two different formulations
proposed until now for AdS_2 quantum gravity. In both cases the theory is the
chiral half of a 2D CFT and describes, respectively, Brown-Hennaux-like
boundary deformations and near-horizon excitations. The central charge c_as of
the asymptotic CFT is determined by 3D Newton constant G and the AdS length l,
c_as=3l/G, whereas that of the near-horizon CFT also depends on the U(1) charge
Q, c_nh \propto l Q/\sqrt G.
