2019 Tourneo Custom wet under battery

[Tbrick18]

I've had a really bad smell in my custom, did some investigation and tracked the source of the smell to wet carpet under the plastic box which houses the battery beneath the drivers (osf) seat.
Everything else seems dry.
Anyone help with this? Where would this water come from? I thought maybe an aircon drain but there doesn't seem to be anything there.

Any help very much appreciated