A123's are charged to 3.6-3.7 v /cell and settle down to approx. 3.45v/cell no load . Lipos are charged to exactly 4.2v/cell and pretty much stay there unloaded . Lipos will drop down to approx 3.6-3.7 v/cell under the light load of a starter/glowplug/pump. The pump itself only draws 1-2 A . The starter and glowplug present the harshest demand on the battery .
I have a data logger that I can hook up next time and get some real figures as the start progresses and then running to full power . Should be intertesting !

BTW if using a lower voltage pack , the voltage must be enough to spin up the motor to the required speed and the Low Batt warnings parameters in the FADEC may have to be changed.

Marc