I don't carry any Alkaline backups................Haven't needed too, reliabilaty has never been a problem. Everybody in my band uses IEMs and we all use these specific 9.6v batteries, there's an initial cost but they pay for themselves rapidly even if you gig/rehearse moderately. A couple of my bandmates are techies, being in ATT's cell phone test division and ex-Microsoft, they checked the Maha ones out pretty carefully and they've more than held up for all of us, I've never had one fail under any circumstances, show or rehearsal. On the day of a show I always just put them in the charger early in the day and they're ready to go in an hour or so, no problem. We play one hour sets so I can easily get two hours use from one battery plus have a few spares, change out is easy.
I let the partially used batteries discharge as much as possible after the show by putting them back in the IEM and leaving it on, back in the charger when I need them again. Simple and again reliable, no complaints here after a year or so.......lots of money saved on batteries, trips to the store to buy batteries, and nothing going into landfills either.
I'll try to find the online retailer I got them from after I get home later today!