For batteries I use disposable CR123As. Consider them like this:
Class 1 batteries are the best quality available and last the longest. These are for my primary light:
DURACELL ULTRA, SUREFIRE, PANASONIC
Class 2 batteries are nearly as good as Class 1, but have slightly shorter run times in my experience:
RAYOVAC, ENERGIZER, STREAMLIGHT, BATTERY STATION
Class 3 batteries are the least expensive, have shorter shelf lives, have the shortest run times, and are best kept as back up batteries or for non-emergency operations like aircraft inspection or training: TITANIUM, TENERGY, POWERIZER
Don't get me wrong, I shop battery prices and get Class 3 batteries all the time (especially the TITANIUM). But I'm a Helicopter Crew Chief and need dependable batteries. In my flight bag I always keep 4 spare CR123A in a powerpax battery caddy, which is in a sealed ziplock bag to keep out dust and moisture. Always keep a light with spare batteries together. Seems like it always fades out just when the operation gets "serious".
In my flight suit I have two lights, currently a Streamlight ProTac HL and a Streamlight Polytac LED. I tape the Polytac to my forearm above the wrist (had too many fly out the open door..lol).
You have to have a light which has a low power setting so that it lasts a long time. I used a Surefire Fury on an operation this week and the body is very slippery. But I see there is a lanyard ring available, I'll get it soon. Both the Surefire Fury and Streamlight Protac HL seem like great lights.