[asid61]

115 recycled batteries perhaps every 3-4 years. Our "competition" batteries were at most a year old and we bought 2 batteries a year, so typically we would have 4 batteries for a competition. Batteries up to 2 years older than that (depending on how well they held a charge) would be used for testing at home, prototyping, and occasionally outreach. So for a LiFePO4 to make sense, we would need them to last around 4x as long due to the cost, which is 8 years of competition and 16 years of casual use.
Given the discharge rating on the LiFePO4 batteries, I'm not sure it would give you that much increased lifespan. Are there ones rated for higher discharge rates that aren't too expensive? I would be interested in these for extended outreach mainly.