I don't disagree with anything said about rechargeables in general, but as for taping in general, and IEMs in particular (the subject of this thread), there is no way I would use a rechargeable product.
I have had multiple failures over the years with rechargeables, and zero failures with new AA batteries. Yes, I check my batteries with quality testers before hand. I do use rechargeables around the house since they came out in 1990, just not for taping. Occasionally I get the bad one that shows good voltage, but drains very quickly. Never had that issue with new AAs.
With the type of show I usually tape, between the ticket, airfare, hotel and rental car, I might have $1,000 wrapped up in the show. If I have a battery failure in the middle of the show, more than likely I won't even know it, unless I am monitoring the recorder feed with ear buds. And even if I do notice it, it becomes very problematic trying to change batteries in the seat and I'm sure as shit not going to get out of my seat and risk venue security seeing an errant wire. Add IEMs into the mix and it becomes exponentially more difficult. I now have a full audience rig and up to 2-4 IEM packs with screwy looking antennas, wires, and red and blue lights that say "bomb" to the woman next to you.
Now if you guys are recording some local cheezy cover band at the local bar down the street, that might be perfect for rechargeables, as who cares if you miss the show. I am not going to risk $1,000 to save 50 cents on an AA battery. I want to remove potential issues from the equipment chain, not create them. AAs are more dependable. Rechargeables are for household use.
Best example? Ford vs Ferarri, this scene:
Lee Iacocca: So, you’re saying it’s challenging.
Carroll Shelby: Look, it’s not even a track, Lee. Le Mans is eight and a half miles of country road. It’s narrow, ungraded. It’s rough. There’s no camber on the turns, no rails. You got to do that for twenty-four hours. Twenty-four hours, Lee. That means night. Half of that race is in the dark, you can’t see shit. Cars coming up on you out of nowhere. Drivers stumbling around the track, pouring blood. Maybe one of them’s your friend, maybe he’s on fire. You’re exhausted, you’re hungry. Can’t remember your name, what country you’re in, and all of a sudden you realize you’re doing a hundred and ninety-eight on the straight. And if anything goes wrong, you blow a gasket, five-cent washer. That’s it, whole thing’s over. Ferrari wins again. Just like it won last year. The year before that, and the year before that.
Yeah Lee, it’s challenging.