On socalrider's advice, I picked up some of the Duracell 2650mAh rechargeable batteries maybe a month ago. I got them at a Target store on sale at maybe around $9 for four of them. I like them as probably just about the best readily available, consumer off-the-shelf rechargeable batteries out there (that is, easy to find anywhere). BUT -- "easy to find anywhere" has much less meaning with good rechargeable batteries because you won't need to replace them regularly. To me, the source is not a big deal since you don't usually need rechargeables "RIGHT NOW." If you find a set of rechargeables is no longer performing up to par, you can re-order your favorites (if you have to get them off the internet) and wait a handful of days for them to arrive (still using your available rechargeables or alkalines in their place, if need be).

I also bought a set of eight Powerex 2700mAh batteries from Thomas Distributing for about $25. I'm loving them, too. Here's link to those (mulchie, I know you already likely know where this page is):

Powerex Batteries at Thomas Distributing

For use with one flashlight that runs on two AA batteries, a four-pack would be perfect. Mulchie, my guess is that you use alkalines in your Mars 3.0 and rechargeables only in your Fenix, so a four-pack of really good rechargeables might be all you'd really need (again, just guessing).

Another thought is this (on purchasing rechargeable batteries after your first set is more or less used up). You might never purchase the same set of batteries twice, unless you're needs are like mine and you have LOTS of devices that run on rechargeables. If you use them in only one or two devices, by the time those batteries are no longer functioning at the high level they once were, the next generation of batteries will likely be available -- and your choice might not even be to go with the same brand that thrilled you with its high capacity a couple of years earlier. (Case in point, a couple of years ago, my choice was for Energizer 2500mAh rechargeable batteries. Now, even though those are still available, there are better batteries out there like the Duracells and Powerex. So, it's doubtful that for my uses I'd ever buy the Energizers again -- at least not the 2500mAh versions).