It's unlikely they will end up in a landfill. A completely spent battery has cobalt, nickel, manganese, lithium, copper and steel which can fetch around $1500 on average. The trick is in how cheaply you can extract those. (The main cost drivers are battery logistics cost, and battery disassembly costs). Fun fact: Spent batteries are categorized as "Hazardous Waste", and need to be transported in explosion-proof containers, with special licenses, and the police needs to be informed of the exact routes that are travelled.

Bias Disclaimer: I'm working at a company (founder) where we build robots to automatically disassemble the batteries and avoid logistics costs.