2S Battery Configurations
 

Seems like I’m seeing more battery companies list the pack configuration in their descriptions. 2s1p or 2s2p. I understand the meaning behind it, but what’s the advantage or disadvantage to one or the other?

For a part it will be related to availability but 2 parallel cells can also have a lower internal resistance.

Generally 2S1P will be more expensive because it's 2 cells total with a larger capacity per cell and less IR with potentially a longer lifespan having fewer internal connections where a 2S2P will have 4 cells total which will increase both the IR and overall weight of the pack. The larger the capacity per cell, the more expensive they are to produce.

Having cells in parallel generally lowers IR.

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.

Higher mAh will give a lower IR. So yes bigger 2S1P packs will have a lower IR due to the mAh increase. But 2 packs in parallel effectively halve the IR.

From the testing I have done, 2S2P packs from the same manufacturer and same overall capacity, when compared to a 2S1P pack, the 2S2P packs will have lower IR.

Now I am not saying you can't get 2S1P packs that have lower IR, but those will cost more. When comparing the same quality cells, 2S2P packs will have lower IR.

As far as longevity, I buy new batteries every season, so I don't really test for longevity.

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.

Interesting you've seen a lower IR with a higher mah, every pack I've tested has been the opposite. This is cycling them on a GFX at 20 amps charge with a 35 amp discharge.

The only time I have ever had a GFX in my shop was when I was working on one for someone. I use the Battery Wizard, which I designed, build, and sell. And I have found that higher Ah packs have lower IR. You can do this by the extremes and look at a 350mAh pack with an IR of 30mΩ/cell then compare to a 4200 2S1P of 3mΩ/cell. But there are more things than just capacity that can affect IR. Heat being a big one. You may not be heating a higher mAh pack as much as the lower mAh pack during discharge, which would lead the lower mAh pack to have a lower IR. I have some 4200 ULCG 2S1P packs that if you discharge at 35A will get hot (130*F), and they will have a nice low IR as well, then a 4400mAh 2S2P pack that barely gets to 110*F, IR is higher after the discharge than the 4200, but the discharge curve on the 4400 is a lot better, and if you take the IR when both batteries are at the same temp and the same voltage, the 4400 has a lower IR. So you have to be careful how you measure IR.

Another thing to consider, higher mAh generally means the battery can deliver more continuous current, if higher mAH batteries have higher IR, that means they would get hotter faster, which means they would be rated for less current.

Edit: to add and on topic to the OPs question. packs in parallel matter. I have 2S1P 5800 ULCG packs that have worse IR given same measuring variables than 4400 2S2P packs, from the same manufacturer. But this goes back to parallel packs having lower IR, not necessarily falling in the capacity argument. So again, lots of considerations...

In general the shorty and ULCG packs have higher IR than typical 260-285g packs. When you get over the 300g range I've seen IR start increasing again. What size packs have you been comparing?

I have purchased lots of batteries over the years and have always cycled my batteries to see when they start to fall off. In most cases large capacity packs have yielded lower IR. The ULCG packs are the worst for IR, amost all ULCG packs are 2s1p config. I'm sure there are exceptions but from my experience the above is trued 90% of the time.

Isn't a GFX a very old charger? I don't think I would trust the numbers coming from that charger. I use a 406duo or DX8 duo icharger for my cycle readings.

So, for context, we're running dirt oval, 17.5 in blinky. At one time, the only thing we were allowed to run were the 5200 50C mudboss packs with a Deans plug. Now, the battery is open to whatever. When I cycle, I look at the 8 volt time, 120 second and 240 second voltage numbers to compare, along with the IR, total discharge time, total mah and average voltage. Basic GFX stuff as well as what the pack looks like on the icharger.

With the mudboss packs, I'd see anywhere from .5 to .7 per cell on the icharger or 1.4 to 1.7 total on the gfx. I'd still be running those now but they're heavy, in the 330 gram range.

I've compared 6500's, 7000's, 8200's and 8400's. These have been R1, SMC, Intellect, EA, Fido as well as some no name brands. Everything but the 7000's were 7.4v packs, with the 7000's being 7.6 packs. All full sized stick packs. In each case, the 6500's always had the lower IR's compared to the other open packs (non mudboss). What Trilerian said makes the most sense to me with the cell configuration and the heat in the larger packs not being as high as the lower mah packs after a cycle, but I always put two cycles on each pack and used the second cycle numbers as the result. They were all done at the same temperature, other than what they gained due to the cycle. When I'd cycle the packs, I'd cycle one pack once, then a different pack allowing the first to rest until the second pack was done then put the second cycle on the first pack.

Overall, just trying to learn more. As I said in the original post, the fact that the battery manufacturers are starting to post the cell configurations with the other battery information peaked my curiosity.

The cell configuration is listed on every battery of mine going back 10+ years, it's not a new thing.

I guess I've just never paid it any attention then.