Is the 1-1.5C with the original setup of 40 Ahr cells? I was unclear when you got the second set of cells if you paralleled them with the original set or not (giving you 80 Ahr cells).
At the beginning of the project I had a 124V nominal lead acid pack.
I bought 16 CALBs (SE40s). I put 8 of those in parallel with 2 12V 29HMs (Sam's replacement for 29DCs). This was my proof of concept just to make sure things went well. It did so I added the other 8 cells giving me 16 SE40s in parallel with the 2 29HMs and 3 8V GC8s.
I planned to run that for a long time gathering data, but ended up finding the cash to do the full booster pack, so I bought 26 more CALBs (CA40s). By this time I had replaced some old lead, giving me a 128V nominal lead pack (13 GC8s + 2 29HMs) and a 42 cell booster pack (16 SE40s + 26 CA40s).
My controller decided it didn't like being overvolted so I pulled 1 GC8 and dropped to 40 cells on the booster, then 39 to improve the balance.
I won't have a 80AH pack until the lead all dies in the next year or two and I buy another 40ish cells to put in parallel. So far I've only used series lithiums in parallel with lead.
The action you described above is only when the car is stopped right?
When coasting or stopped there's a balance current between the packs, sometimes one way, sometimes the other. Now that I've again found a good balance point it's very small, and is nearly 0 within a few minutes.
$1.50 an Ah seems to be about standard yes? Most of the sites I see has 40 Ah prismatics in the $58-$60 range which is just under $1.50/Ah. I've seen Headway 40152S 15 Ah cells for $23 which is about $1.53/Ah. I'm not so sure there's that big a price difference buying smaller cells. Consider if you were starting with 160 Ahr cells. They seem to be running about $210-$220 a cell. You can get 150 Ahr by tying 10 15Ah cells together. The cost at $23 each would be $230. So the total cost of a 36x160Ah stack is $7560 while the 360x15Ah setup is $8280. The total energy is 19 KWh vs. 17.8 KWh for a final $/Wh cost of $0.39/Wh vs. $0.46/Wh. But the second stack can be purchased as 10 individual $828 strings while the entire cost of the 160 Ah stack would need to be capitalized in the beginning.
I'd consider $1.25/AH to be a decent price for CALBs. Depending on the supplier the price/AH can be the same for small as large cells. Mine were cheaper and other prismatic brands are cheaper. Headways are more, and they've gone up instead of down; I wouldn't consider using A123 or other pouches because of the assembling hassle, same for non-threaded cyllindrical cells (some headways and many other brands).
While I think headways could make a great booster, I don't think you'd want to go that route for a full pack unless you really need C rates over 10. I think the few who have done full headway packs have said they wouldn't again. 360 cells would be a huge pain to connect, and I've heard they don't stay balanced as well as the prismatics, so that'd be another pain/expense.
I have access to 12Vx35Ah U1 wheelchair AGMs at $25 each. For $750 it's possible to put together a 12.6 KWh SLA stack in a 120Vx105 Ah 10S3P configuration at a weight of 750 lbs. Now I agree that adding less than 2 Kwh of Lithium isn't that helpful to range. But what are the effects in terms of buffering the deep discharge current when accelerating? What effect would that have on the range since the Peukert effect is lessened by Lithium string.
That could work. I'm not too familiar wth AGMs, but I doubt wheelchair batts are designed for much current. For comparison, my original pack was 10 125AH DC29s for ~$850 and lasted about a year.
I think my 12V batts are around a year old now, so unboosted they'd be about dead. I need to start doing an unboosted run every 1-3 months to see how they hold up on their own. Also for the reduced Peukert I need to get more meters connected and do a good range test.