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Subject:
From:
Steve Hackney <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steve Hackney <[log in to unmask]>
Date:
Wed, 13 May 2015 13:17:51 +0000
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Thanks Wayne.

Sorry about the confusion - the cycling I was referring to was operating cycles of the device that is powered by the battery. Not discharge/charge of the battery - we are using it in a normal "start new, run it until it's dead" fashion.

Regards.

Steve Hackney
SmartWave Technologies

-----Original Message-----
From: Wayne Thayer [mailto:[log in to unmask]] 
Sent: Wednesday, May 13, 2015 9:15 AM
To: [log in to unmask]; Steve Hackney
Subject: RE: [TN] Alkaline batteries

Hi Steven-

I recently did a whole bunch of tests on "AAA" alkalines. Never saw what you've seen: All of the cells I worked with dipped rapidly below 1.5V in the first 10% of consumed life (and during this initial period, the ESR actually DECREASED slightly before rising somewhat as you state--but note that the ESR is HIGHLY temperature dependent). But I did get kind of amazed as to the variations in performance and the implied tradeoffs for the mechanical/chemical design of the batteries. There's a huge compendium of data out there for the "AA" batteries: www.batteryshowdown.com

Your reporting of life in cycles for an alkaline is new to me: Are you saying that these are rechargeable alkalines? I've no experience with those. I'm used to life in mA-Hr.

Wayne

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Hackney
Sent: Wednesday, May 13, 2015 8:52 AM
To: [log in to unmask]
Subject: [TN] Alkaline batteries

I know that this is peripheral to the topic of electronics, so if this is a breach of etiquette I apologize But… we are having some challenges with alkaline batteries and I am wondering if anyone has had a similar experience at some point, and perhaps can give enlighten me. 

We are seeing dramatically short battery life, but the failure mode is a little unusual. Normally I see the open circuit voltage (Voc) drop steadily with use, at the same time as the internal resistance gradually rises, until eventually the combination reduces the voltage under operating load and the battery is effectively dead. 

Now I am seeing the open circuit voltage basically unaffected (i.e. 1.5V per cell), while the internal resistance is VERY high. So the batteries have no current-generating capacity, and can’t drive the operating load.

Does anyone have any suggestions as to what might cause this behavior? I can think of all kinds of things to do to kill batteries, but they always affect the Voc at least as much as the resistance.

Some specifics:
-	Alkaline D cells
-	Brand name, from a reputable manufacturer, with a good track record in the past
-	There is no problem on the application side (the devices being powered are within specification, consistent with past performance, no current spikes and so on)
-	For reference purposes, we normally see starting Voc at 1.5V and internal resistance maybe 0.2R per cell. At end of life, we would expect Voc around 1.0V and internal resistance around 0.6R.
-	In this case, we are seeing Voc at 1.5V and internal resistance 1.0R to 1.5R, with about 5% of what we would call normal life usage (i.e. 2000-3000 operating cycles out of a normal battery life of maybe 60k cycles)

Any ideas? What would you do to alkaline cells to get them to behave like this? I suppose it could be a problem on the battery manufacturing side. But I would welcome any brainstorms or suggestions.

Thanks,
Steve Hackney

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