Topic: 9V battery weirdness

[WiFiJeff]

I have been using standard alkeline 9V batteries to power some of my gear, especially my DPA MMA6000 preamp.  Over the years I have used a few different brands, usually getting about 20 hours on the MMA6000 (with powering of DPA4060 mics) before the green blinking light turns red, which is generally a sign that I have about 3-4 hours left before it goes dead.  Recently I picked up a lot of Rayovac "Heavy Duty" 9Vs with a 5/15 use-by date.  I noticed I was getting more like only 10 hours before I got the red light, last night the problem got to me, and I decided to see if the red-light warning time was still 3-4 hours (I always change out as soon as I see the red light to avoid losing anything).  The red light blinking MMA6000 ran overnight for over 9 hours before I shut it down.  When the red light starts blinking, my battery tester shows one or zero (of five) indicator lights, so it thinks the battery is shot just like the MMA6000 sensor. 
Do "heavy duty" cells have some kind of different chemistry and see a voltage decline earlier?  Since I want to dump the 9V cell as soon as the warning light appears, putting most of the cell's life during a warning period is not optimal for me.  Is this just a bad batch?  Has anyone seen anything similar?

Jeff

[dnsacks]

per rayovac website (http://www.rayovac.com/Products/Heavy-Duty-Batteries/9V-1-Pack.aspx), these are zinc chloride batteries which are optimized for low drain uses (think smoke detectors that will run a year on the battery).  Per http://www.greenbatteries.com/battery-myths-vs-battery-facts-1/#Misleading, it looks like alkaline batteries have 3x the capacity of zinc chloride (which looks to roughly match your observations).  So, looks like you're getting what you're supposed to out of these and I suspect that differences in the zinc chloride discharge curve is causing the long run time with the warning light blinking.

[Gutbucket]

dnsnaks beat me to it when I got distracted while typing- 

'Heavy duty' typically indicates 'old-school' zinc-chloride or zinc-carbon chemistry which is different than that of an alkaline cell.  The discharge curves of each of these are different, just like the discharge curve of NiMH is different from that of alkaline, which people tend to be more familiar with around here since recorders often have alternate settings for those.  The alkaline cell has more of a plateau in the curve and the zinc-carbon or chloride drops more linearly without the plateau and I suspect that's the primary basis of the difference you are seeing.  If I recall correctly, those cells doesn't hold a charge as long as alkaline cells in storage either, so if they are somewhat old they may already be somewhat lower in Voltage to start with.

FWIW, I've never used standad or heavy-duty cells in it, but I get about the same run time as you with the MMA6000 on alkaline cells.  I also use the low-self discharge 9.6V Maha Imedions in the MMA6000 but have never done a run time test with those.  Seems at least comprable to alkaline cells though.

[WiFiJeff]

Thanks!  There is no indication on the packaging that these are zinc chloride, but it doesn't say alkalide either.  They have had one positive factor: some alkalides have been unreliable in the MMA6000, dying without warning but then coming back to life.  I use Imedion AAs in other devices (Sony D50, Nagra Lino, Sonosax MiniR82, SD MP-1 etc) so maybe it's time to try the 9.6V ones, since your experience seems to be that the current output is sufficient.  Is the MMA6000 red warning light dependable with these?

Jeff

[Gutbucket]

The 9.6 Voltage doesn't hurt, but I don't think its important for this application, I just happen to have those batteries on-hand since I use them in my ther gear.  When I last replaced those I was happy to see that they are now available as a Low Self Discharge version, which I do think is important.  After not having used the MMA6000 for years, I pulled it out last year and have been using it to power the 4098H mics.  I haven't run-timed it poweredy by the Imedion 9.6Vs, or run it once the light goes red.  I didn't notice a significant reduction in run-time before the light goes red though, and only found it in that state testing things before a recording date and just swaped out the battery.