NiMH batteries about 2600mAh sized. You must be careful not to go bigger as they may not fit the transmitters.
This type of battery will get stronger at about the 10th charge-discharge cycle.
The battery warning LEDs will not be accurate with this type of battery as the chemistry of it discharges at a different rate.
...But most of us really loathe
them, Jeff !
Not just because of the way they'll "self discharge" at an alarming and "non-metered" rate between your twice weekly usages, but also because of the discipline that they'll impose on each and every user for them to have a chance at surviving for anything like their rated number of cycles ...and I'm not talking about just XD-V use, but use with ANY
"mission critical" electronic gear.
...Buying new batteries every month or so could be quite costly...
In practice, my friend, ...not really.
Having an accurate
"fuel gauge" that flashes a genuine "forty minutes to go red warning" when using alkalines means that replacements are far fewer and (maybe even more importantly) far easier to schedule
than you'd initially expect.
Rechargeables' nasty habit of reading "great, ...still great, ...plenty of time to go" and then only flashing a warning minutes from total collapse is a truly major pain in you-know-where.
Also, buying "ten and twenty packs" of non-counterfeit "Duracell" or "Eveready" from reputable high-turnover outlets (be they supermarkets or hardware outlets) renders the cost comparable, or maybe even cheaper, than nickel metal-hydrides, ...even when going for the "premium" or "ultra long life" versions ...and bearing in mind that, unlike rechargeables, those alkaline AAs typically have a shelf life in excess of ten years