Where it is most troublesome is things that require 4 batteries or more. Rechargeables lose 1.2 voltes off the bat in a 4 cell device.

Since lithium cells usually have over 1.5 volts, could I slip one lithium in with 3 lower voltage cells somewhat safely? Or would this just be asking for leaks, fire, loss of hair and looks of disdain by my neighbors?