I thought the typical landfill in the US is willing to accept lithium batteries, but putting a Tesla battery pack in a landfill is economically dumb compared to selling the used pack to someone interested in recycling the raw materials in the pack.
That means that putting the battery pack from an 85 kwh Model S in a landfill is equivalent to putting a stack of over 300 $20 bills in a landfill.
(He was actually trying to make a point about how cheap battery packs might be to buy new in the future, with more efficient techniques for turning the raw materials into battery packs.)