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I wonder if the CR2 gives much more usable energy than 2x LIR2450. If my numbers are right, the CR2, typical capacity is 800mA (to 2V), so the amount of energy is around 2J (2.5 * .8). On the other hand, the LIR2450, has a capacity of 100mAh (to 3V), so the amount of energy is around 0.37J (3.7 * .1) each - or 0.74J for two.

However, the volumes of the two are roughly the same: 2x LIR2450 is 4524mm^2 whilst CR2 is 4595mm^2.

Is my analysis correct?

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  • \$\begingroup\$ No, you have omitted the all-important "h" in a couple of places i.e. 800 mA should read 800 mAh. You have also used the average voltage of the battery to calculate things. In fact, for accuracy you need to determine energy levels as the voltage drops. There may be other errors. \$\endgroup\$ – Andy aka Jun 16 '17 at 12:34
  • \$\begingroup\$ and the chemistry is slightly different for LIR vs CR. \$\endgroup\$ – ammar.cma Jun 16 '17 at 12:36
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CR2 average voltage during discharge will be around 3V http://www.varta-microbattery.com/applications/mb_data/documents/data_sheets/DS6237.pdf

LIR2450 will be around 3.7V (average) https://www.powerstream.com/p/Lir2450.pdf

(Random datasheets linked)

Essentially you are correct in your analysis that a CR2 should give you more energy density than two parallel LIR2450s - but then the LIR2450 cells are rechargeable. The LIR2450 has less size so a greater % of the volume is taken up by the casing which is a large contributor to this difference, but then so is the chemistry, as they are different batteries, its not apples and oranges but its close.

The discharge rate of your application will further effect the observed life and capacity greatly - so the quoted mAh is rarely seen in high discharge. Additionally for low discharge applications the self discharge rates will vary (but I cannot see from my quick look at the data sheets, its often not quoted).

So in summary without buying three batteries and testing there will be an amount of speculation over capacity, personally I prefer in these scenarios to buy the different batteries and test with a dummy load that represents my actual load, or the load itself to determine what is the best fit for me, as its easy and cheap to do (unless your expecting lifetime in the years, obviously).

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