Thanks Louis. I like your guess, it makes a lot of sense.

Apologies for the "R" - this is my bad-habit shorthand for "Ohms."

Steve Hackney
SmartWave Technologies

-----Original Message-----
From: Louis Hart [mailto:[log in to unmask]] 
Sent: Wednesday, May 13, 2015 9:23 AM
To: TechNet E-Mail Forum; Steve Hackney
Subject: RE: [TN] Alkaline batteries

Steve, my simplistic picture is that 'open circuit voltage' is a function only of the electrochemical couple. Any instrument will present some load, so true open circuit voltage can't be measured.

I don't like guessing, but cells/batteries are relatively simple. My guess is that they are starved for electrolyte and thus have high internal resistance. Incidentally, I do not understand the use of 'R' in connection with internal resistance.  Depending on how the batteries are tested at manufacture, I believe cells with high internal resistance could escape detection.  They may not be tested with the kind of load you have.

I have not taken apart many cells, but have noticed wet aluminum electrolytic capacitors do not contain much electrolyte. I could not squeeze a drop from the separators in most versions of them.  I suspect manufacturers are trying to use the minimum amount of electrolyte that would get the job done.  It's what I would try to do.  Louis Hart

-----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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