Rechargable Battery Fit

[Ocsac]

My county school system performing arts center produces 8 three-night shows per semester and 4 community shows in summer. I'm about to place my third (or is it fourth?) $500 battery order of the year. I probably have a case for switching to rechargeables. We use Sennheiser EW-D and Shure SLX (not SLX-D). I'd like to experiment with rechargebles for 1 of each of those systems during the summer. Before I place an order, I have questions.
1 - Standard AA rechargeables are larger in diameter. Will they fit in our SLX and EW-D? My tech crew are trained, competent and experienced high school students, but I don't want battery swaps to be too "fiddly". Ansmann Slimline are an option, but significantly more expensive.
2 - Is my assumption correct that the nominal voltage difference (1.5V vs 1.2V) is not a problem? The discharge curves look similar, but I expect the battery health meters will read differently, especially on the SLX. I need about 5 hours battery life on the actors.
3 - I haven't yet run the numbers on recharge cycles needed to break-even, but I'm interested in your experience, and anything else I may be missing.
Thanks!

 

[themuzicman]

I've been using nothing but rechargeables for over a decade now. The gold standard on Broadway and touring theater has been Powerex Pro batteries, coming in at $94/8 with charger at the link I attached, or $27 per 8 AA and $80 per charger via Powerex's website. They are rated for 500 cycles, we typically run two sets of batteries on a single set of chargers on a larger show and replace every 18 months or so to err on the side of caution (8 shows a week, 52 weeks a year, that's 416 cycles in total not including weekly put-ins or other rehearsals). We color code each set with nail polish just for ease of distinguishing what's last nights set vs tonights set easily if things get commingled. The more judicious A2's I work with test every cell with a pulse load battery tester as sets get on in age just to verify capacity. With your more limited use, with proper conditioning cycles they should last a few years.

With proper charging before every performance, assuming you're using fully charged batteries you should get 6+ hours out of every set, no mid-show battery swaps required unless something has gone awry.

1 - Standard AA rechargeables are larger in diameter. Will they fit in our SLX and EW-D? My tech crew are trained, competent and experienced high school students, but I don't want battery swaps to be too "fiddly". Ansmann Slimline are an option, but significantly more expensive.

I haven't had issues with rechargeables fitting in things in a number of years. I haven't touched an SLX in a while but my guess is that you'd be fine, they work in every other piece of Shure equipment I've touched.

2 - Is my assumption correct that the nominal voltage difference (1.5V vs 1.2V) is not a problem? The discharge curves look similar, but I expect the battery health meters will read differently, especially on the SLX. I need about 5 hours battery life on the actors.

Nominal voltage difference is fine. The battery telemetry back to the receivers will be off due to the difference in discharge curves and higher starting voltage if there is no menu selection for Alkaline vs NiMH but otherwise it's all good.

3 - I haven't yet run the numbers on recharge cycles needed to break-even, but I'm interested in your experience, and anything else I may be missing.

Let's assume you have 16 microphones - 8x EW-D and 8x Shure SLX for a total of 32 AA batteries.
For PowerEx you'd be looking at $376 plus tax for an initial set plus chargers and a secondary set of AA's would be $108 for a grand total of $376 plus tax and shipping.

I haven't bought ProCells in a minute but a quick google is telling me that a case of Duracell ProCells is around $75 for 144 cells (via Amazon) or around
$0.80 from a distributor, for a cost of $115 a case. I'll go with the lower estimate for this example. At $75/144 you're paying about $0.52 per cell, which would mean you'd be using 722 Alkalines to get even with a purchase of rechargeables - or 22 performances of those 16 wireless mics used in the example.

You'd break even on just your 8x 3 night performances alone, not including the rehearsal process.

 

[Jay Ashworth]

Yeah, sure the voltage difference will be a problem.

The usable power in a battery is the number of mAh you can pull out of it between *the starting voltage of the battery* and the *cutoff voltage OF THE DEVICE*, set in the firmware or hardware to protect the batteries you put in.

Since the starting voltage moves down from 1.5V to 1.2V, that's a lot less voltage drop to the cutoff voltage in the device, which does not change. Now, sure, different chemistries will have different amounts of under-load-voltage reduction per mAh drawn, but will that be enough not to cause you to need to own, and change, batteries much more frequently in operation?

I'm not sure there's any way to project that; you'll probably just have to test.

I *can* tell you that if you're going to, say, 2300-2500mAh NiMH rechargeables, those things are VERY sensitive to being dropped, since the layers are so much thinner; my experience in digital cameras was "if you drop it, it's done". Yes, at all. Yes, at any angle, even on carpet. You drop it, it's gonna short, and its life just got cut in half, or worse.

 

[gafftaper]

I've been using rechargeable Enloop Pro AA batteries in my Sennheiser EW's for about 8 years with no problems. I have four Tenergy TN160 - 12 battery charging trays so I can charge 48 batteries at once.

No reliability issues. No regrets. I have about a hundred of them so I can have two full sets of batteries. In non-show conditions I have measured well over 10 hours of life. I can easily do two dress rehearsals, but I always swap them out in between shows. I would guess some have been in use up to about 5 years. I usually lose about 8 a year. I've never had one get old and suddenly unpredictability loose charge. They always just stop recharging (probably because they took a little too hard of a hit as @Jay Ashworth described).

 

[gafftaper]

Here's a link to my original post when I first got them.

 

[Ocsac]

themusicman: Thanks for the battery, charger and battery management tips; I knew choices made here would make all the difference. I didn't expect anyone to actually do the math for me! Economically it's a no-brainer in my situation.

@Jay: Point taken that it's the cutoff voltage if the specific device that matters. I expect the Sennheisers will be fine but I'm going to start small with the SLX and see how they behave for a couple shows. If they don't, I'll work the rechargeable $ benefits into a case for accelerating the transition to newer units. Also the batteries vulnerability to impact shocks - my student techs will be fine if they know the issue. The biggest problem I have when handling batteries / micing actors is when we are pressed for time and directors / choreographers step in to "help".

@gafftaper: I wondered about attrition, your experience gives me an idea of what to expect and how to gauge if it's normal, or if I'm doing something wrong. We run 16-20 mics and I like the idea of having 2 full sets. Thanks for the link to the previous discussion.

It took me awhile to respond, been working 10-12 hour days prepping to open Jekyll and Hyde tonight. At our level of theatre, everyone does a little bit of everything!

 

[gafftaper]

@gafftaper: I wondered about attrition, your experience gives me an idea of what to expect and how to gauge if it's normal, or if I'm doing something wrong. We run 16-20 mics and I like the idea of having 2 full sets. Thanks for the link to the previous discussion.

Yeah I try to maintain two sets plus about 10 extra so I'm always ahead.

 

[Craig Hauber]

My county school system performing arts center produces 8 three-night shows per semester and 4 community shows in summer. I'm about to place my third (or is it fourth?) $500 battery order of the year. I probably have a case for switching to rechargeables. We use Sennheiser EW-D and Shure SLX (not SLX-D). I'd like to experiment with rechargebles for 1 of each of those systems during the summer. Before I place an order, I have questions.
1 - Standard AA rechargeables are larger in diameter. Will they fit in our SLX and EW-D? My tech crew are trained, competent and experienced high school students, but I don't want battery swaps to be too "fiddly". Ansmann Slimline are an option, but significantly more expensive.
2 - Is my assumption correct that the nominal voltage difference (1.5V vs 1.2V) is not a problem? The discharge curves look similar, but I expect the battery health meters will read differently, especially on the SLX. I need about 5 hours battery life on the actors.
3 - I haven't yet run the numbers on recharge cycles needed to break-even, but I'm interested in your experience, and anything else I may be missing.
Thanks!

Why aren't you using the actual Sennheiser li-ion battery packs for the EW-D's?
-I didn't think you could buy them without? The pack fits perfectly in the transmitters but they made it capable of holding 2xAA for backup use. I've never had to because the rechargeable packs far outlast any show I've done (8+ hours)
And in the last 3 years the cost savings on batteries has been very significant.

 

[FMEng]

I don't know about Sennheiser, but Shure battery packs and chargers are expensive. It is much cheaper to use rechargeable AA batteries and put up with the inconvenience. If you have the budget, the packs save a lot of time.

 

[gafftaper]

Why aren't you using the actual Sennheiser li-ion battery packs for the EW-D's?

Looks like the list price on a two port battery charger and two batteries for an EWD is $150.
The Batteries for my EW 100/300/500's are more like $80 each without the charger.

or
you can use the rechargeable gear I've been using for years:
Tenergy 12 port AA Battery Charger: $35
and
12 pack Panasonic Enloop Pro AA Batteries: $60

I have 20 Sennheiser Microphones kits of several generations (EW 100 G1, EW 300 G3. EW500 G4, and EW-D). I keep about 96 batteries in stock. That's two full sets of batteries so I am confident I can make it through a two show day with no issues. Plus spares so I can jump back and forth between handhelds and belt packs if needed. Cost me about $620 when you add on 4 charging trays.

 

[chausman]

I don't know about Sennheiser, but Shure battery packs and chargers are expensive. It is much cheaper to use rechargeable AA batteries and put up with the inconvenience. If you have the budget, the packs save a lot of time.

Different than live theater, but in a theme park environment we found the ROI on Shure rechargeable to be about a single summer season. Plus the significant ease of use. And they have a built in storage function for the off season.

 

[Ocsac]

Follow-up: Picked up a Powerex charger and batteries for our Senn EWs. Tested them in the old Shure SLX, and I don't know what their cutoff voltage is, but they run 5 hours without issue. The MH-C980 shows them taking 900 to 1100 mAh (love that feature of the charger!). So we bought chargers and two sets of batteries plus extras for everything. Been handling them myself so far; when I finalize the management & tracking I'll train the techs, including the "dropped battery" caution. (Makes me wonder if the acrobatic dance group might affect them with occasional falls, etc). Thanks to all for the input.

 

[Jay Ashworth]

Follow-up: Picked up a Powerex charger and batteries for our Senn EWs. Tested them in the old Shure SLX, and I don't know what their cutoff voltage is, but they run 5 hours without issue. The MH-C980 shows them taking 900 to 1100 mAh (love that feature of the charger!). So we bought chargers and two sets of batteries plus extras for everything. Been handling them myself so far; when I finalize the management & tracking I'll train the techs, including the "dropped battery" caution. (Makes me wonder if the acrobatic dance group might affect them with occasional falls, etc). Thanks to all for the input.

I suspect you'll be ok if the batteries are ensconced in a pack.

It's a much sharper shock when one end of the cell hits the ground while the other is still moving; that is apparently what causes the interlayer shorts that kill the battery.

You probably do want mic belts for that though; flying packs are no fun in any event.