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Could there be some practical issues when operating a lithium-ion battery pack that consists of cells all in one line? (for instance, at a +/- series connection, individual cells within the first parallel unit no longer share the same distance through the conductor to the middle point of the second unit)

Example for 2S2P: Schematics of the 2S2P cell connection in square vs in line

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    \$\begingroup\$ The in-line topology might work better at higher powers, because there is less interior volume for heat to be trapped. \$\endgroup\$
    – rdtsc
    Commented Jan 31, 2022 at 20:42
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    \$\begingroup\$ If you move your supply wires to the 'outside' ends of the connecting Ni strips, then you again have the same total distance through them for every cell, assuming your top and bottom strips are the same gauge. \$\endgroup\$
    – Neil_UK
    Commented Jan 31, 2022 at 20:43
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    \$\begingroup\$ I think the problem you are worried about (regarding the nickel strip) will be small compared to the problem you will have if the cells are not exactly matched. \$\endgroup\$ Commented Jan 31, 2022 at 20:53
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    \$\begingroup\$ As @ElliotAlderson suggests, lithium cells, in particular, require some charge equalization mechanism to protect cells in series-connected battery from extreme over-charging or reverse-charging. Failure to do so causes early battery failure, and possibly fire and rapid, unscheduled, self-disassembly. \$\endgroup\$ Commented Jan 31, 2022 at 22:01
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    \$\begingroup\$ The only difference I see is cooling. \$\endgroup\$ Commented Feb 1, 2022 at 3:10

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The answer depends on which parameter you consider. Obviously, it makes no difference to the volume. Assuming the cells have exactly identical internal resistance, capacity and self discharge current:

  • Resistance: in line is slightly higher
  • Thermal: in a square is somewhat better because all the cells cool equally*
  • Degradation: in a square is better because the cells cool equally and therefore degrade at the same rate; in a line is better for the two outer cells cool more than the inner cells, but unequal degradation between cells is not desirable, so I go back to: in square is better
  • State of Charge: in the short run, they are the same because because dynamic changes in current do divide exactly equally in both cases, out of symmetry. In the long run it doesn't matter because cells in parallel equalize their SoC naturally.
  • Self discharge: in a square is better because the cells are at the same temperature

However, each of these is of secondary effect. Matters of mechanical fit prevail.

*) Keeping the cells at the same temperature is more important that increasing their cooling in an asymmetrical way.

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