Near-Extremal Black Hole Evaporation in Asymptotically Flat Spacetime
  We study black hole evaporation of near-extremal black holes in spherically reduced models with asymptotically Minkowskian spacetime, with the effects of the back-reaction on the geometry included semi-classically. The stress-energy tensor is calculated for null in-falling observers. It is shown that the evaporation proceeds smoothly and there are no instabilities of the outer or inner apparent horizon before the endpoint of evaporation. 
Kamran Diba and David A. Lowe