I thought 0.5grams seemed too light also, I have the Energizer AAA's in several devices, and they are light, but, not that light. I took a look at the Eveready site. They list the weights on their chart:
L92 AAA Lithium battery: 7.8 grams.
E92 AAA Alkaline battery: 11.5 grams.

Personally, I think shelf life is really the big winner for Lithiums, at least for your survival, long storage emergency lights. Also, I believe they handle cold better, although I saw an earlier post that seemed to question that. They are lighter, but, virtually all AAA bat's are pretty light anyway.