Using Rechargeable Batteries

*From my article originally published in CAS Quarterly, written January 2007.

Using Rechargeable Batteries for Production Sound

For the past year {2006-2007}* I have been making the switch from primaries to rechargeable batteries for most of my power needs in both my ENG bag system and my regular location and studio cart system. I began using rechargeable NiMH AA’s in my slates, and that was so successful I felt encouraged to expand the practice.

NP1 batteries power the entire portable rig. However I also use iPower USA 9V Lithium 500 mAh batteries in my Comtek transmitters and receivers, as well as in all of my 400 series Lectrosonic wireless transmitters. NiMH AA batteries juice my 442 Sound Devices mixer as backup power.  I highly recommend the SANYO AA 2700mAh NIMH cells. I use them in my slates and the 744T.

For my 744T recorder, which I use in both bag and cart, Sony Lithium Ion rechargeables have been great, while in my “old school” Soundcraft mixer 10K mAh NiMH D cells give days of usage before needing recharging.

Perhaps a little unusually, there is no quad box on my cart. One of my goals is to operate free from hard line power whenever necessary. A large rechargeable battery pack powers the entire cart. NP1 batteries and a BDS (Battery Distribution System) power the Lectrosonic receivers.

For most pieces of equipment I have three sets of batteries. This way there is always one set ready to go, one set on charge (which takes 2-3 hours), and one set in the units. The 9V Lithiums have a very low self discharge rate. Comtek receivers do fine with 2 sets. They last considerably longer in use than they take to charge.

Nickel/Metal Hydride Batteries

NP1 Batteries and Charger

One of the consequences of using so many different sizes of batteries is the need to carry and have available numerous different chargers. All the different machines go on to the follow cart and are placed in the care of the Utility Sound person. The MAHA model MHC808 eight bay multi-size charger for AAA, AA, C and D sized cells has been invaluable during the shoot.

Also essential to success is a reliable battery tester. The ZTS is the only tester which accurately tests Li-ion batteries, and works with all the batteries that may be used on the set.

Using rechargeables is good economics, both for me and my producers. Standard Ultralife (up to 500 mAh) Lithium primaries cost about $5.25 each. 9V Lithium rechargeables cost around $15.00 each but are good for at least 200 cycles vs one cycle and then into the trash. The iPower 9V Lithium batteries are serialized so it is easy to keep track of them, and rated to 300 recharge cycles, making them extremely economical.

I always write the first date the battery is used on the cell, in order to anticipate the replacement date. If a battery is used regularly, the expectation would be replacement after one year of use. NiMH and lithium cells should be disposed of properly at a recycling center. Often your equipment vendor is a collection point.  

Probably the greatest deterrent to the widespread use of rechargeables is the fear of sudden failure or drop off. Initially I monitored the battery voltage very carefully, as I continue to do with my wireless receivers. Over time I became more confident with my system operation, and now I have a good feel for how long the charge will last, while still erring on the side of caution. I have avoided problems by changing out my Lectrosonics transmitter batteries after about 4 hours of use.

I will add that although a lot of people do, I personally have never used Alkalines in my 400 series (because it is not recommended to do so) therefore I can make no comparisons between them and the rechargeables in those units.

Larry E. Fisher of Lectrosonics highly recommends using rechargeable over primaries in any of their products. He says, “Rechargeables are now as good as primary batteries. The only battery that is better is the disposable Eveready Lithium AA. A few years ago I couldn’t say that, but battery technology has advanced quite a bit.”

Lectrosonics has been engaging in fairly extensive comparison testing of rechargeables’ performance, and the company is planning to ship rechargeables with some of their new equipment.

According to Fisher, Lectrosonics is shipping the AA NiMh Eveready 15 minute charging system with the SM, SMD and SMQ transmitters. He says, “A quality 2500 mAh NiMh AA battery will run the SM for over 4 hours, the SMD for 8 hours and the SMQ 1/4 Watt for 6+ hours.” 

He adds, “We will ship the iPower 9 Volt Lithium Poly Ion (lithium polymer ion) batteries and a charger with the UM450 transmitter units as a standard item.  The iPower battery actually has more capacity (500 mAh) than the best 9 Volt alkalines in our units. They work very well at low temperatures and can deliver the high currents for our 1/4 Watt UM250 series. This will be the only battery that we recommend for them.”

More information about run times and actual user experiences can be found at the Google newsgroup RAMPS where Fisher has posted about Lectrosonics battery tests. Another site that has a lot of info on AA rechargeables, an aptly named “NiMh shootout”, is Candle Power Forums.  There is also a lot of helpful data at the Lectrosonic FAQ page.

Fisher is sympathetic to concerns about unpredictable drop offs.

“I can understand the hesitancy to use rechargeables since they have been notorious for failing at the worst time. I can also understand that a fresh primary battery is 99.99% reliable and I would certainly use one in an absolutely critical application,” he says. “I think sound mixers should try the batteries in low risk situations to gain confidence in the performance of the new generation of rechargeables. I’d still keep primary cells around for those make or break situations.

“It does take a little more care to use rechargeables. You’ve got to keep track of what batteries are charged or discharged and you have to make sure the charging cycle was completed. Eventually you have to throw the older batteries away as they lose capacity. None of this is rocket science but it does require a little more organization.”

Rechargeables are also recommended for all their products by Ralph Belgique of Comtek, and products are in development to extend the use of integral rechargeable batteries through using jacks for charging.    

According to Belgique, “The receivers and transmitters all have charging input through either the audio earphone output jack on the receiver or the Aux input jack on the transmitters. We are developing a charger that will allow the [iPower 500mA Li-Polymer type] battery to be charged through the earphone jack or Aux input like the Ni MH and should offer more that twice the operating time of the Ni MH.”

Again reliability is one of Belgique’s greatest concerns.  

“The long term reliability of the Li-Polymer type battery is really based on the type of charger used and the discharge rate.  Li-Polymer batteries are more delicate than Li-Ions which are normally used for industrial types of applications (such as cell phones). So the charger becomes a very important part of the reliability of the battery.  Time will tell if the Li-Polymer batteries will hold up under the vigorous environment of the motion picture industry, but we are willing to give it our best shot to try to use them.”  

The earth friendly nature of rechargeable technology is the greatest side effect. Over my career I have taken hundreds of pounds of used up 9 Volt, AA, D and CR123A cells to the hazardous waste collection facility at the Dockweiler Sewage Treatment Plant, so that they wouldn’t end up in a landfill. I am probably the exception to the rule in this since I live nearby; I’m sure most mixers don’t have the time to lug copious quantities of used batteries to a safe and relatively environmentally sound end.

Instead of using up the massive resources needed to create all of these disposable batteries, I have chosen to use rechargeable and recyclable technology. At the end of my last job, I did not have a single battery to discard.

While initially expensive, the switch over to rechargeable technology has already paid for itself many times over. The bottom line is that the use of rechargeable batteries on movie sets is an idea whose time has come. It is something to be embraced not feared. This really is a win-win-win action we can all take.

Leave a Reply