Yep, I am paranoid too, and use a fresh Li-ion rechargable battery at every gig. I keep a spare fully charged right at hand. To date I have never had to change a battery during a gig. I have changed a few during practice, but I tend to let the battery sit in the Zendrum until it runs dry if I'm not playing a gig. What a difference running wireless, and with the right batteries. Wireless and regular batteries was not a great combo; even regular rechargable had a limited life. Now, even though I come prepared, I haven't had an issue.
But, let's talk about cables, lol! I was setting up for my last gig and even though all my lights were showing that the wireless module was working properly and the Zendrum was triggering, I had no sound. Speakers on? check. Turned up? check. i went through a preflight checklist, and nothing came up empty. So, I decided I better go tethered. I got out my merge box, and plugged a MIDI cable in to the back of my module, and suddenly had the idea to try that cable with the wireless. Sure enough, it worked! I had a bad MIDI cable! First time that's happened. Tested it with an ammeter tonight, and as I was testing ( I took the ends out), I saw my problem... a broken wire at a solder point where it attaches to one of the pins. I have to solder it. Should be an easy fix, but everything is so small! I need a magnifier, and reading glasses, lol! And, I just ordered a couple of spare 5 footers, they are really cheap. Not sure it's worth fixing the old one, other than to say I did fix it! Ah well, can't hurt to have a few backup cables I suppose. :-)