I made a mistake with my pack voltage calculations. different manufacturers have different cell volt info and I got in the weeds. so I reworked it and the 144s LTO pack is perhaps a very close match to the 96s LiPo pack at important voltage states. The LTO idea I'm talking about is replacing the 48x 7.5v, 65ah 2s2p modules with 48x 7.2v, 3s2p modules of nearly equal physical size. the cells I link to are not the right shape, I was just trying to show the market availability. From a packaging perspective the stock 2012 modules are 303x213x55 which is 3716cc per module and there looks to be space to expand the cell foot print a little, maybe an inch longer. the amp hour capacity of a 6 LTO cells that could fit into the 4100cc maximum envelope for each module would be about 48 amp hour, for a pack power of 33kwh.
the primary idea of this thread was to talk about replacing the cells in the battery with anything else. I still like the new 37ah LiPo plan with liquid cooling. the prototype 2s3p module is going to happen.
You would want a completely revamped BMS. Not only because of different cell voltages, but also would need to handle cell balancing, charge tapering and more. Reverse engineer or license from Nissan the communication protocol to the rest of the car.
As I corrected myself the overall pack volts are perhaps closer than I first though, so would a new BMS really be easier? nearly all market-available BMS' are less than 100a and don't get close to 144s without a scary stack of daughtercards daisy chained together. are we talking about a custom designed BMS? know an EE? also, do other new Nissan cars have the ability to be interfaced with non OEM canbus parts? I was operating on the assumption that Nissan will never help a person or a business interface with older leaf's, because they want to sell new leaf's, or that's the vibe I get reading this forum. while I've never worked with Nissan, my experience in automotive engine control systems is that even the larger tuning houses, AVL, Roush, FEV and the like cannot interface with OEM computer system without inside help. the people who do get stuff to work use open ECUs and toss the OEM computer.
I understand the risk of not using a cell balancing BMS for LiPo cells, as they burst into flames at the slightest provocation. hoverboards right! but even in the stock 2012 2s2p LiPo pack there is not protection for the 2 parallel cells, that's less than ideal for sure and we accept that risk. according to the web sources I've read, LTO cells do not explode and burn when crushed or short circuited and can recover from a 0v discharge. so the risk of a dead cell would be reduced capacity until the faulty cell was replaced and it would show up on LEAFspy as one or two low cells before it got there (the BMS would think its 96s so it would group up to 2 serial cells together in the readout). and the 144s arrangement of 48x 3s2p modules would still allow balance current every three series cells. just brain storming here with the LTO stuff, thanks for the good leads!