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I have looked at car jump starter packs and found something peculiar. Almost all of them are three lithium cobalt oxide cells in a series.

This seems odd to me. I have understood that lithium cobalt oxide batteries have a rather short lifetime and are mainly useful for energy density, something which car jump starter packs do not require. Car jump starter packs are relatively heavy for the energy they contain, but are optimized to provide a huge amount of energy in a short amount of time.

To me, it seems like a better configuration would be three NMC (nickel-manganese-cobalt) cells in a series, three NCA (nickel-cobalt-aluminum) cells in a series or four LiFePO4 cells in a series.

According to battery university, lithium cobalt oxide cells only have 2/4 rating for lifetime and specific power, whereas NMC and NCA have 3/4 rating for both, and LiFePO4 have 4/4 rating for both.

I understand that some jump starter packs indeed are based on LiFePO4 cells. But those that are not, are almost always lithium cobalt oxide and not NMC or NCA.

Why is that? Do NMC and NCA have some inherent weakness when used to provide huge currents in a very short time?

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Probably because 4 LCO cell in series have a higher voltage than a 12 V lead acid battery (4 * 3.65 V = 14.6 V), forcing lots of current from the Li-ion jumper battery into the lead acid battery? As opposed to using a battery with 4 LFP (LoFePo4) cells in series (3.2 V * 4 = 12.8 V) which would be ideal to slowly charge a lead acid battery. Three NMC in series, as you suggest, have too low a voltage: 11.1 V unloaded, probably about 7 V when cranking an engine.

Having said that, my understanding was that car jumper batteries used LFP cells, not LCO cells. But I'll take your work on that.

Starting a car is hard on Li-ion cells, whether LCO or LFP, because they are discharged at a high C-rate.

While it's true that Li-ion cells for high power applications tend to use a chemistry other than LCO, you can't generalize that LCO cells are inherently unsuited because cell design can be optimized for power applications or for energy applications.

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