  Freudenthal duality is, as of now, the unique non-linear map on
electric-magnetic (e.m.) charges which is a symmetry of the Bekenstein-Hawking
entropy of extremal black holes in Maxwell-Einstein-scalar theories in four
space-time dimensions. In this paper, we present a consistent generalization of
Freudenthal duality to near-extremal black holes, whose entropy is obtained
within a Jackiw-Teitelboim gravity upon dimensional reduction. We name such a
generalization near-extremal Freudenthal duality. Upon such a duality, two
near-extremal black holes with two different (and both small) temperatures have
the same entropy when their e.m. charges are related by a Freudenthal
transformation. By exploiting Descartes' rule of signs as well as Sturm's
Theorem, we show that our formulation of the near-extremal Freudenthal duality
is analytical and unique.
