Mark,
Gen1 cells should not be used. They are known for not holding capacity well and in general are very aged. The Alphard has Gen2 cells as standard within. You can replace cells with other gen2 cells however please note the ECU tolerances for each of the 15No. blocks is very tight.
Swapping out cells is bad engineering practice, you will just make the next set of cells the weakest. Furthermore you overcharge the better cells to charge up weaker cells, making them expand and dissipate excess energy as heat. Heating up the whole pack and getting caught in a cycle.. killing itself faster.