For those that have used a DC pre-heater with a lipo pack, how many heat cycles do you get from an average sized (5000mah or so) battery?

A lot of variables! Ambient temperature, how long you pre-heat for, which device your using etc. generally though on a 3s 5000mah lipo I use I get a good 60 minutes of heat time before I charge. That probably translates to 5 cycles on my competition heat deuce 2.