Agreed, you have to charge and discharge once to measure with precision the
coulombic efficiency, but if you are not doing research you don't
necessarily need to do it more than once.

If you understand how a population of batteries behave regarding coulombic
efficiency, you can simply apply the damaging high state of charge and
temperature and after you have accumulated the same overall time as a many
cycle regime, you could estimate whether a test specimen is within

Or you can take samples from different sources and make comparisons without
resorting to many cycles.

One of Dahn's salient points is that below some threshold of SOC% and
temperature, you are accomplishing nothing to stress the battery. The only
reason to cycle low is to check the capacity.  Then he goes on to show how
much "accelerated life testing" never actually exposes the cells to
significant. damaging conditions. 10000 fast cycles could have very minimal
time or none ate levels of SOC% that cause harm.  The test sounds good on a
website, or spec sheet, but reveals nothing useful.

If you try to get information on salient test conditions from a
manufacturer or worse, a distributor, you may never actually talk to anyone
who is knowledgeable, or see graphs with labeled axes, and so on.
Comparisons are nearly impossible because test conditions are not

A big user like Tesla, for instance, gets involved in HPCE (high precision
coulombic efficiency) testing because it is currently the only way to make
rational decisions in a timely manner.

But many cycles of charging should be minimized to levels depending on the
decisions to be made. Development and quality control require different


On Fri, Oct 14, 2016 at 6:48 PM, Roger Stockton via EV <>

> Measuring the coulombic efficiency requires cycling the cell(s), as what
> one is interested in is how much of the energy delivered to the cell on
> each charge cycle is *not* recovered on the subsequent discharge.
> Cheers,
> Roger.
> _______________________________________________
> Read EVAngel's EV News at
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