Why do RCR123 cells have lower capacities?

[Black Rose]

While reading the I can't believe people pay $10 for CR123s and the cr123batteries.com thread, rechargeable CR123 solutions were mentioned as the best way to keep costs down, which is true.

While I was reading those threads, in the back of my mind I was thinking "Yes, rechargeable CR123 cells are a great idea but their capacity sucks in comparison to primaries". That combined with the fact they are rather expensive when buying quality cells is what has kept me from buying them.

Then I got to wondering, why is the capacity of RCR123 cells low (Li-Ion is around 750 mAh and LiFeP04 are at 500 mAh for quality cells).

What are the technical reasons that these cells cannot have higher capacities?

 

[EngrPaul]

In simple terms, primaries are designed with as much energy density as possible for single use. The chemistry can be completely tuned to delivering energy once. To design a cell to be rechargeable, other things need considered to allow energy delivery and restoration, resulting in less capacity.

When you're comparing batteries, be sure to multiply the nominal voltage times the mA*h, so that you get mW*h. This will give you a clear picture of the energy storage potential of a battery, and a good prediction of the runtime on a regulated light.

 

[mdocod]

As EngrPaul has noted, comparing the mAH capacity of cells that operate at different voltages has no meaning.

And then the other problem is that, you can compare based on label capacity for RCR123s, they are all very exaggerated.

A CR123 might have ~3 watt-hours capacity, while a 3.7V RCR123 tends to have ~2 watt-hours capacity. While a LiFeP04 RCR123 is closer to 1 watt-hour capacity (maybe a little higher )

Another consideration is that most 3.7V RCR123s are going to have a protection circuit at the end of the cell, so they have to make the actual CELL smaller, to make room for that PCB.