Originally Posted by
billdelong
I don't think that's the case when comparing a single cell of the same rated capacity.
For example,
1S1P of 5Ah
vs
1S2P of 5Ah
I believe the single cell at 5Ah will offer lower IR
I do agree that when both 2.5Ah cells are combined together in parallel to make them 5Ah, it will reduce the IR compared to a single 2.5Ah cell, but they won't get as low as the single cell of 5Ah even when they are same rated quality. Idea being that the loss of IR will be due to the additional wiring which may start out pretty close when new, but will drastically degrade faster with the 2P configuration where parallel wiring because lower capacity cells will degrade faster as compounded loss degradation. The more cells wired in parallel will degrade exponentially faster because you are introducing the higher probability of weaker cells forming.
From all the packs I've seen of comparable Ah rating, the 2P variants have lower IR. But it's pretty unusual to find a 1P pack with the same capacity as a 2P pack, usually the 1P packs have lower capacity and a slimmer profile.
As for the extra wiring, those wires will usually be in parallel too, which will reduce effective resistance of the wires.