OGITC makes great points as usual. Even if you wanted to keep the same overall battery bank capacity, you could do 2 parallel14s25p packs. That puts each 25p cell block at 400Ah. Balancing will be a little bit faster, and won't stress a BMS as much. Of course, you'll need more BMS equipment -- cell monitors, etc. The individual cell blocks will also be about half as heavy when you are heaving them around and so forth.
My Leaf-based pack is built in a rolling steel computer server rack cabinet. For perspective, it comprises the full battery packs out of TWO Nissan Leaf vehicles, plus a couple of spare cell modules -- so you're talking about a lot of battery. After stripping off the factory Nissan casings and extraneous equipment, then reconfiguring the modules into the 14s14p setup I needed, plus adding back in the weight of the server cabinet -- I believe the pack's overall weight came in somewhere in the ~750lb range. I can roll it easily on the concrete shop floor, although I rarely have any reason to move it more than a foot or two.
There's a random lesson here... I didn't build my battery in the shop where it is deployed -- which was sort of stupid on my part. (On the other hand, I had power and air tools available in the old shop where I assembled it, and at the time I had no power in the new shop where it now resides...which was the whole point of the project.) When I needed to move the finished battery from the old shop to the new shop, I just used my tractor forks to pick up the entire server cabinet and plop it back down a half-mile or so away in its new location. With the overall weight you are talking about, let me humbly suggest that you plan ahead better than I did, or else that you happen to have the tools and equipment that I was lucky enough to have on hand!! Moving this thing by hand (without fully disassembling it) would very easily be a several-man job.
Finally, just to throw one more sub-thread into the conversation -- have you thought about capacity testing the Spim08 cells before assembling them into larger packs? I'm not sure how "new" or "used" your source would be, or how consistent the cells which you receive will be, etc. There are various schools of thought on this, but the general consensus is that each block of paralleled cells needs to have about the same capacity. (In other words, each of your 25p or 50p blocks in the 14s string needs to have about the same Ah of capacity. We're talking actual / tested capacity here, not rated capacity when new.) There are a couple ways to approach it, but they all basically come down to fully charging each cell and then discharging it, measuring its capacity during discharge. After you have an actual reading for every cell, you can build up your parallel banks so that they are all capacity-matched. Again, sorry to cloud your question, but that's something worth thinking about ahead of time -- because it will require a bit of extra planning, equipment, and considerable time to test as many as 700 cells. If you're already building an 18650-based pack, you are probably already familiar with this line of discussion.
Cheers, John
