Hmnnn, I think obscure batteries that are hard to obtain in regular circumstances are not going to be any easier to obtain during an emergency. And one hopes that you've already stocked up on batteries in advance. (I certainly have!)

Now, if you modded a 6 D cell MagLite to take a 9V Cree, you'd have my attention. (And you could probably cook with that thing too, so it does double duty.) But a regular MagLite is a something of a joke compared to a modern 2xAA flashlight.

I do have a number of D's stocked up for radio usage but I found it fairly trying keeping every kind of battery around the house. Much easier when you can share them among devices.

P.S. For completeness sake, it should be noted you can buy 8,000 mAh rechargeable D cells, but you'll have to get a special recharger for them and they are expensive.