How much of a drop are you seeing? Voltage should remain fairly steady (+-1V), although the AMPS used during that cycle increase dramatically.

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car