Using Rechargeable Batteries For Wireless Microphones.

I was asked recently about using rechargeable batteries for wireless microphones. I discovered that I have two completely different opinions on the topic:

1) What I say I believe: There’s no two ways about it: batteries are expensive; 9v batteries are the worst, but even AA batteries aren’t cheap in the quantities we need for a largely wireless church stage. Current professional rechargeables are up to the task, and NiMH is a competent technology. Consumer rechargeables only produce about 7½ volts on their best day, so we don’t go there, but Pro batteries can power nearly all wireless well for at least a couple of hours.

I never really liked the memory challenges with NiCad batteries, but with nickel-metal hydride (NiMH) batteries, the batteries are more reliable. However, some manufacturers, like Shure and Lectrosonics, still don’t like using any rechargeable 9v batteries, though they’re not as fussy about rechargeable AA batteries; apparently there are enough differences in the batteries and in the wireless technologies that use them that AA rechargeables aren’t so evil. Fortunately, many wireless manufacturers have moved to AA technology.

2) What I really believe: I don’t use rechargeables for my own church’s wireless, and I have six or eight wireless systems. (I just did a quick survey: nobody here uses rechargeables in their own or their church wireless systems.) A couple of our reasons:

a. Power Curve: Rechargeables drain non-linearly. Alkaline drains linearly. That means that an alkaline battery, when it nears the end of its lifespan, is still usable. You know it’s getting tired, because you’re getting a few dropouts. It’s frustrating, but it’s not the end of the service. When a rechargeable battery starts to go, you have a few seconds until it’s completely dead. If that happens 5 minutes before the service is over, you’re toast, whereas with an alkaline, you can easily cope for that last few minutes.

b. Battery life: Because of the non-linear power curve, an alkaline battery lasts for up to 5 or 6 hours in a wireless. Since my church can run 3 hours (including sound check), rechargeables are a challenge. (Consumer grade rechargeables last a matter of minutes.)

c. Convenience: To make rechargeables work, you need to be more disciplined than I am. You need to take batteries out of all wireless after every service and load them into the rechargers (professional rechargers, not Radio Shack toys), and then re-load back into the wireless before the next service. If you don’t use pro rechargers, they’ll overcharge the batteries left in them for the intervening days; this is not a minor detail, but it’s outside of this conversation.
In addition, you’ll really need to plan on replacing the entire lot annually. They might be good for a couple months more, but I hate the uncertainty.

d. Redundancy: If you use rechargeables, you still need to have a handful of alkalines handy for when (not if) the rechargeables fail.

e. Cost: If you’re comparing consumer grade rechargeables to retail alkalines, there’s a huge advantage for rechargeables, but that’s not the comparison for us. We need to compare pro grade rechargeables (including pro chargers) vs. bulk industrial grade alkalines such as CCI sells. The cost is much closer, and – at least in our opinion – not enough to justify compromising the services.

CCI sells (and I buy) the industrial grade alkaline batteries, which are essentially re-packaged Energizers (sorry, no pink bunnies included) and Duracells (likewise, without copper tops). I buy them in case lots and they’re less expensive than Costco batteries, and they're certainly more convenient to use and store. I have several customers who order thousands at a time; we can talk about those prices if you plan to be in that league, but we do stock those quantities.

Update: Since this article was written in 2010, Ansmann has come out with some rechargeable batteries that have proven incredibly reliable. These, I can use.

© 2010 Used by permission. Permission granted to re-post this article on church or tech-related blogs provided that contact information is included.

David McLain | The Wireless Guy | CCI SOLUTIONS
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Olympia, WA 98507-0481
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Nickname unavailable said...

I am lucky - my wireless receiver has transmitter battery status, so the sudden deterioration is easier to plan around (if I bother to look at the gauges during setup).

I still don't trust rechargables, though. The self-discharge on them is a killer for me, because it is weeks and months between wireless setup usage, and nothing but lithium cells stays fully charged for that long.

Tim Gibson said...

I highly recommend that you check out Mike Sessler's series of post about rechargeable batteries. Several church tech directors have now switched to rechargeables based on these posts (including myself).

Mike Sessler said...

I'd like to make a couple of observations. Tim already linked to the testing results I did a few months ago. Those interested can read the in-depth results. But here are a few highlights.

Battery Life In my testing, a ProCell lasted about 9 hours in a Shure UHF-R (with an audio signal hitting the mic for the first 7 hours). The worst rechargeable battery lasted over 11 hours, the best for almost 14. We now put them in on Saturday about 1 PM and use them for rehearsal and service (about 6 hours), charge overnight and then run them Sunday morning for 6-7 hours. I've not seen a mic drop below 4 of 5 bars on the meter.

Convenience If you don't care about wasting money and filling the landfill, you swap alkalines every day worth of services (or after rehearsals). If you do care, you stretch them, hoping they last the weekend. With rechargeables, I know how long they'll last, and run them as such. I don't even worry about it any more.

Cost I figured we save roughly $500-700 annually in battery costs the first year (after a $250 investment to get enough batteries and charging stations to work for us). The batteries I buy are rated for 300-500 charging cycles, which should be about 3-5+ years. Replacing all my batteries will cost less than $100. So worst case, I save $400/yr. Best case, I save over $3,000 over 5 years. And yes, I used to buy ProCells in bulk for under 35¢ each.

I've been using rechargeable batteries in wireless mics for over 4 years and have had excellent results. They are not magic any more than alkaline cells are magic. Use either within their operating limits and either will serve you well. Rechargeable batteries will, however, save you a whole lot of cash.

M Crowe said...

Great notations Mike Sessler, and I totally agree!! You can now get rechargeables for wireless equipment only that have the voltage up front.

IdiotZoo said...

A fairly old post I know... but thought I'd share my experience. We use all ni-mh cells for our radios. The higher capacity AA ni-mh available will power our Line6 handheld for over 5 hours before it registers lower on the meter. We start each service with freshly charged batteries. Never a problem. Saved a lot of money and I'm completely confident in the setup. One thing I will say, is I replace the batteries annually as they do tire with age.

While the discharge curve is different with alkalines, many modern wireless mics will actually get more life from a ni-mh because of the lower internal resistance.

Daniel Patterson said...

What rechargeable batteries and stations are you using?

cherylthecomposer said...

What about lithium batteries? How well do they hold up?

Richard C. Lambert said...

The Leaf had a poor thermal management system and Phoenix was simply too hot a climate for the cartravel batteries