I am not sure what a Scout is in the first place, unless it is the Halcyon light that looks like the old Oceanics, and I carry three of them on dives where I might have to deco in the dark ( 3rd one in pocket for that purpose). 

At one time we carried a second small primary with a 35 watt bulb and nicads to back up the old 5 hour halogens, but we have been running 13 hour lights ever since then and no second primary. 

The backup lights have a few basic rules : they must not be used for anything but backup ( hence the segregated 3rd light), they must have a focused beam good enough for your dive buddies to see you signal mixed in with their primaries ( assuming dive buddies who are paying attention), they must have no switches, they must have replaceable batteries, they must be of a voltage that matches battery and bulb, not overdriven so they don't blow when you need them most, they must be three c cell in line with a twist on bezel, they must have a straight attachment point, they must be stowed DIR, they must be deployed properly, and they must tested and voltage checked before the dive. 

I know you guys all like to talk about stuff, and I know that everyone likes to reinvent the wheel, complicate things, make their mark, etc etc, but the best bet is to do what I did all along - go to the pros and find out what they do and why, and save yourself the bs. Backup lights are serious things, and I can tell you serious stories of very serious uses of them in situations where any CF would have been a death sentence.