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I'm developing a product that uses LTC Li-SOCl2 batteries, a D-cell bobbin type.

I would very much like to be able to take an unclear battery from my desk or some old/demo device and get an idea of its state of health. Is that theoretically possible? Does anyone have experience with a tester device?

Coloumb counting is suggested everywhere, but I want to measure a case which I have not been following through its lifetime.

I know that the passivation changes the battery characteristics during storage/low load, but I think this should be doable still! I can't find a product though so now I'm not so sure...

Here's my idea (perhaps someone could go build me the product I'm looking for? :D )

  1. apply a load to melt the internal oxidizer (it's ok to waste a little bit of energy to get a reading)
  2. then measure internal resistance and temperature
  3. possibly use one of the many proprietary algorithms from IC vendors that do dynamic loads and measure recovery rates etc
  4. compare to known performance
  5. get approximate SoH

Am I oversimplifying? Or missing something?

Alexander Ohm
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1 Answers1

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The simplest method is to monitor the output impedance "over time" (Would be best if the capacity is measured as well). So you can't get a reliable SoH with an instant (or a single set of) measurement. That's probably why you couldn't find a device/equipment for this purpose.

... but I want to measure a case which I have not been following through its lifetime

Measuring and recording the impedance measurements over time (i.e. for days or months) then comparing the results internally (i.e. see if the impedance value stays the same or increases over time on a particular battery) gives an idea about the battery's current SoH i.e. if the battery is still healthy or degrading or dying.

Impedance tends to increase on degrading/dying batteries and and an increase on the slope is an indication of death.

I can't say if it'd be acceptable to compare the measurement results to those taken on a known-healthy one i.e. Having a single measurement result higher than that of a random healthy one doesn't mean a degrading/dying battery.

Rohat Kılıç
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