I asked a battery expert, why the D100 eats AA's. He explained why and I didn't understand a thing he said. So I asked to explain it in grade one english.
Basically, The power curve or level needed to operate the D100 on A A's has a drastic increase in power need like a high spike every time you hit the shutter. You can use AA's till they appear 'dead' then put them in a gameboy or calculator and use them for a considerable amount of time.
He went on to say with a factory fresh set (either type) and you took pictures one right after the other (with auto everything) they would last for 30 50 pictures only, maybe.
He guessed that the reason for the AA caddy was for emergency use. once your EN3's need charging you could use the caddy to get you by but not with rapid photo taking.
He went on, and translated he said two EN3's at once will give you more juice than using two - single EN3. If you use two EN3' at once the will drain collectively.
I am not an expert but what he said did make sense. Hope this helps.
Oh, one more thing he said if you want to carry the caddy around loaded you should keep it in a baggie of some type. Possible fire/shock hazard
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