Based upon what went on with Auto Tires in the US 30+ years ago, they will build up in many people's yards (especially in low populated areas) for decades until it becomes a kind of minor super-fund site.

Unless disposing of batteries can seem "free" and very easy, I expect that to happen. Somewhat similar to used auto oil. I suspect in various places used oil is either burned for heat or dumped in an undeveloped area.