I was wondering that as the difference in the voltage you desire vs. the voltage source increases, does it decrease the efficiency of the circuit or have any disadvantages if you were to put a buck-up (booster) module?

For example, a 3V battery needing to supply a 9V load versus a 6V battery supplying a 9V load.

The flow would be: Battery ---> Boost Module --> Load.

 

Depends on the design of the converter circuit and component used. A poorly built one might see a huge efficiency drop going form 6 down to 3 volts input while a good one might stay well above 90% all the way through.

Also, circuit power draw has a lot of influence in the overall efficiency so if you have a converter that draws 5 ma at idle and the circuit it powering only draws 1 - 2 ma full tilt your overall efficiency is terrible. But if your converter draws 50 ma powering itself at full tilt and the circuit being powered draws 500+ ma your efficiency is very high.

 

Look at this site and play with the design calculator:
http://www.ti.com/ww/en/simple_switcher/index.html

 

Thanks for the helpful replies! Appreciated.