Between the 502 and 502d, if you're using primarily at night, I'd definitely go for the 502d. The key difference is color temp (the d is warmer), and CRI (the d produces light closer to the color reproduction of sunlight). Both of those mean slightly fewer lumens. But, if you really want greater output and/or greater runtime, a spare battery or an 18650 light will be in your future. For me, I've learned to always go higher CRI when I have the choice; and, go warmer for a light intended for nighttime use.
I have a friend who has the 502d and loves it, but as soon as he tried my old h52fw, he wished he got that instead. In your shoes, as you want it for reading and general tasks, I would recommend the h53fc. It will be significantly brighter and be more useful for lighting up things further away than a couple of feet in front of you. It will work really well for reading too, and you can use a lower setting for better battery life compared to the h502 series. If you are leaning towards a mule/full flooder, I would recommend you jump to the 18650 h604c to get more lumens and more versatility. This is my opinion. The h502 will be beautiful for close up tasks, but as soon as you want to see a little further, you will feel the need to get a different light. I owned a 502 and sold it shortly after getting it because I much prefered my h52fw as an all around do it all headlamp.
I'm an AA survival person as well, but never do anything other than single cell. I never want to have to rely on having 2 cells working when it might end up I have only one. And if one dies, I just switch cells. I never have to worry about having 2 good cells at a time. I use all eneloop AAs.
Carrying an Eneloop in the light and a lithium primary AA as spare is about perfect weight wise, if you only expect to use one Eneloop.
Or carry a spare Eneloop if you expect to need it,
and a couple Energizer Ultimate lithium AA as backup.
The point being to not use the expensive and light weight lithium primaries, but have them if needed.
Here's a trick:
Take one of those 6 bay AA battery organisers made by Storacell, and cut it into a 2 cell holder and a 3 cell holder... you lose one of the bays in the process of sawing, whittling and sanding, but you get two sleek spares carriers out of it.
I use this with AAA personally, as minimal AAA twisty lights seem to me to complement 18650 better than AA.
I'll usually carry an Eneloop and an Energizer in the 2 bay, or two Energizer;
the 3 bay holder tends to stay at home.
I agree NPL, the newer H53Fc looks about perfect for general use... getting a pure flood means ordering another light soon.
No big deal, the pure floods are neat too, great garage, crawlspace, and work bench lights.