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On rechargeable batteries for high profile RF mic/IFB/IEM use

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Dave Stevens:
This is taken from the "where do I get cheap batteries thread" and Mac if you think it needs to be integrated into that thread please do.  This is direct experience from almost 3 years on large scale modern human circus style production shows on the Strip in Las Vegas.  In addition to being one of the all around mixer type dudes at the  show, I'm also what is called the "battery czar".  I ride heard over the rechargeable batteries used for 158 radio IEM/IFB packs on 22 freqs as well as batteries for 22 radio mics.  We are presently migrating out of the 700mHz band (to the tune of well into six figures for our show alone) and will go to all rechargeable batteries when the move is complete just after the first of the year.  We currently are using 9v and AA rechargeable and were planning on using AAA NiMH but suspended the transition as the new mic packs are the 5200 series and use a single AA.  Once the migration is complete we will eliminate the use of alkaline cells in all of our radio gear which includes more than 200 Motorola radios, 16 UHF hoist controls and 52 BTR 800 packs in addition to the IFB/IEM and mics.

We currently use the Sennhieser Panasonic NiMH sleds and charging system in the G2 series listen packs but most of our inventory is 3000 series with G1 style packs.  The 9v are the iPower Li-polys that are at Thomas distributing.  We stock and manage an inventory of just over 200 iPower 9v in the show at any given time.  At this point only 16 of the packs are G2 series AA but it will change to all AA G2 series style packs soon.  I've done extensive testing on AAA NiMH, AA NiMH, 9v NiMH and 9v Lipo cells and have documented run time and overall cell life.  We use a Fluke 199C with computer logging interface and a jig I made to plot use curves in real world conditions.  

To be short, we haven't found any 9v rechargeables with quite as long a run time as alkaline 9v.  To compensate we use two rotations of batteries swapping them for each show.  We have calculated a savings of about US$15,000 per year using this method for 9v cells alone.  There are issues with an out of the box or within a couple week failure rate of about 12% but we can usually test and segregate those cells prior to failure during the performance.  We have more ear piece failures than battery failures due to the extreme conditions in which they are deployed.  We try to rotate the lipo cells out every six months or so as they seem to deteriorate after that though we do have some cells that are more than a year old.

In testing and real world performance we have found the AAA and AA cells operate as well as alkaline in our applications.  You do need to condition the NiMH cells periodically and make sure they don't get "soft" but routine testing and maintenance will take care of it.  We consider our technical, artistic and creative standards to be among the best in the industry.  If we are able to use rechargeable cells in these apps I see no reason why others can't as well.


Mac Kerr:
Dave, thanks for sharing the results of your research. Can you share what you have found to be effective "conditioning" of rechargables? That is quite a battery inventory you are dealing with, how do you keep track of bad cells?


Andrew Broughton:
Dave, thank you for supporting what I have been saying for years about rechargeables.

I'm curious if you ever tried the PowerEx batteries and chargers?

Mac Kerr:
Dave Stevens wrote on Wed, 10 December 2008 16:44
 We consider our technical, artistic and creative standards to be among the best in the industry.  If we are able to use rechargeable cells in these apps I see no reason why others can't as well.


It may be because your technical standards are high that the system works for you. In a facility situation like your's, even though you are at the sharp end of the stick, you have tight control over the handling and maintenance of the batteries. I fear that in the area of one offs like I deal with day to day it would mean relying on the shop for that quality control, which may not inspire confidence. There may also not be time for battery charging when rehearsing or in show mode from 7am-6pm. Batteries can charge overnight, but during the day there may be a large demand. Keep us informed this is an important issue.


Scott Helmke (Scodiddly):
It works because the company is in complete control of the batteries, as Mac says.  As more of a rental house there's no way we could manage that.  People would be throwing away our batteries to put in alkalines, or at the absolute best not keeping track of things well enough to make the system work.

It's great that it can be done, though.


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