I had a single AA size Energizer Ultimate Lithium battery sitting around (like the one pictured right) and decided to run a little test with it. This isn't super formal but it is informative nonetheless. I used one of my non-LCD chargers as I am currently running test on the few LCD chargers that I have out, so the discharge was not constant current, only into the on board resistor which is 3.9Ω. Either way it gives a general idea of the discharge characteristics between Lithium (blue), NiMh (orangish-red) and Alkaline (gray). The thing to note here is the higher voltage the lithium maintained during discharge than the other two, which in this case means it was actually delivering more current into the load. As you can see it also lasted quite a bit longer than the others. So why don't we all switch over to using Energizer Ultimate Lithium?... well first off they are expensive but more importantly they are only one time use. So except for when you wont be able to recharge batteries or when you want a really long shelf life (like in emergence equipment or something) then I still think that most of the time a good set of Low Self-Discharge NiMh batteries are the best choice for AA and AAA battery needs.