  We show that primordial (nearly) extremal black holes with a wide range of
masses from the Planck scale to around $10^9$ g could be cosmologically stable
and explain dark matter, given a dark electromagnetism and a heavy dark
electron. For individual black holes, Hawking radiation and Schwinger discharge
processes are suppressed by near-extremality and the heaviness of the dark
electron, respectively. In contrast, the merger events of binary systems
provide an opportunity to directly observe Hawking radiation. Because the
merger products are not extremal, they rapidly evaporate and produce transient
high-energy neutrino and gamma ray signals that can be observed at telescopes
like IceCube and HAWC. The relationship between the near-extremal black hole
and dark electron masses could also shed light on the weak gravity conjecture.
