Every one seems to have their favourite brand, Steve...

But I've found that the consensus amongst most pro audio folk veers towards Duracell (available bulk packed as "Procell") and Eveready Energizer.

The only "no-no, ...NO!" with any Line 6 transmitter is the use of carbon-zinc "standard" AA's, (even if claimed to be "heavy duty") as your transmitters' performance will suffer.

In any case, when the sums are done, the considerably higher endurance of alkalines over "standards" very often results in the alkalines proving to be cheaper.

Watch out, though, as I've found that "bulk direct" from both of the above companies can be both dearer and less fresh than their "blister packs" of ten and twenty from local chain stores. (Truly bizarre...)

As for me, I mostly rely on Duracell alkalines, whether badged as "Procell", "Ultra", "Super" or anything else, but I have no qualms whatsoever about running a similar variety of Energizers, both of which give at least 7, but usually eight (sometimes up to nine) hours of continuous transmission at the higher (10mW) power setting.

If, like me, you have occasional gigs where either you're unsure of the overall duration required, or access for a battery swap may be difficult, you CAN buy roughly 24 hours of continuous transmission in the form of very expensive lithium AA's. (With any luck, you can pass the additional cost on to the client...)

Doing so means you forgo the use of Line 6's "fuel gauge", as lithium's will indicate as having "full" capacity until a few minutes before total collapse.

(Lithiums are also really great for still supplying current at freezing temperatures that will "kill" cheaper types.)

I recommend "quarantining" these batteries from transmitter duty as soon as they've completed a session, as there's no way of knowing how long they'll run next time.

As a result, my world includes quite a few toys, (...for all ages, ...I'd better omit any details... ) clocks, torches and remote controls that are running on ridiculously over-rated batteries!

Finally, I have encountered some folk who are happily running rechargeable nickel-metal-hydrides, (NiMH) albeit having been forced to adopt a similar discipline with respect to the consequent inaccuracy of the "fuel gauge" system.