If you are more than a ‘guy with camera’ you know how important off-camera flash is; especially on sunny, cloudless, days. This article deals with battery performance for external camera flash units (‘speedlights’).
I would like to point you to this 2 minute video on the Maha Energy website that shows you the astonishing performance benefit of NiMH battery over alkaline. Not only do NiMH cells out perform alkaline type, they will pay for themselves and a good charger very quickly.
It is extremely important that you use a good charger with your rechargeable batteries. If you have been experiencing crappy battery performance or battery life, it is probably the fault of your charger. Most drugstore / fleamarket battery chargers charge for 14 hours whether the cell needs it or not. A proper smart charger is the best thing for your rechargeable cells.
What about lithium-ion battery technology?
Li-ion batteries are the choice for laptop computers and electric cars because they can pack so much energy into such a small space. And that is exactly why they are dangerous… because they pack so much energy into such a small space and once they catch on fire, there is no way to extinguish the fire. This is why it is getting more difficult every year to fly with devices which contain li-ion batteries. It is already very difficult to ship them by “next day air” shipping services.
I expect someday soon we will see speedlight manufacturers jump on to the li-ion fad. Be assured, I will not be buying one of them, it just will not be worth the expense and difficulty.