Its VERY unusual for a battery to just leak.
I sold loads of them for 15 years and only ever saw one leaker.
Before there is any negotiation, I'm sure the supplier will want to inspect the battery.
Usual caused are over filling, over charging, putting the battery down on a stone and puncturing the case, or - as did for most Mk3 escorts - rain water leaks onto the battery and washes the tray with acidic water on a regular basis.
Good Luck.