  We construct the holographic dictionary for both running and constant dilaton
solutions of the 2D Einstein-Maxwell-Dilaton theory obtained by a circle
reduction from 3D gravity with negative cosmological constant. This specific
model ensures that the dual theory has a well defined ultraviolet completion in
terms of a 2D CFT, but our results apply qualitatively to a wider class of 2D
dilaton gravity theories. For each type of solutions we perform holographic
renormalization, compute the exact renormalized one-point functions in the
presence of arbitrary sources, and derive the asymptotic symmetries and
conserved charges. In both cases we find that the scalar operator dual to the
dilaton plays a crucial role in the description of the dynamics. Its source
gives rise to a matter conformal anomaly for the running dilaton solutions,
while its expectation value is the only non trivial observable for constant
dilaton solutions. The role of this operator has been largely overlooked in the
literature. We further show that the only non trivial conserved charges for
running dilaton solutions are the mass and the electric charge, while for
constant dilaton solutions only the electric charge is non zero. However, by
uplifting the solutions to three dimensions we show that constant dilaton
solutions can support non trivial extended symmetry algebras, including the one
found by Comp\`ere, Song and Strominger, in agreement with results by Castro
and Song. Finally, we demonstrate that any solution of this specific dilaton
gravity model can be uplifted to a family of asymptotically AdS$_2\times S^2$
or conformally AdS$_2\times S^2$ solutions of the STU model in four dimensions.
The four dimensional solutions obtained by uplifting the running dilaton
solutions coincide with the so called `subtracted geometries', while those
obtained from the uplift of the constant dilaton ones are new.
