  We consider the low temperature quantum theory of a charged black hole of
zero temperature horizon radius $R_h$, in a spacetime which is asymptotically
AdS$_{D}$ ($D > 3$) far from the horizon. At temperatures $T \ll 1/R_h$, the
near-horizon geometry is AdS$_2$, and the black hole is described by a
universal 0+1 dimensional effective quantum theory of time diffeomorphisms with
a Schwarzian action, and a phase mode conjugate to the U(1) charge. We obtain
this universal 0+1 dimensional effective theory starting from the full
$D$-dimensional Einstein-Maxwell theory, while keeping quantitative track of
the couplings. The couplings of the effective theory are found to be in
agreement with those expected from the thermodynamics of the $D$-dimensional
black hole.
