My airbag light has come on. Checked it with IID tool and it says Battery Disconnect. I reset it and cleared the fault but it's come back on again.

What is meant by battery disconnect in relation to the airbag and why is it still faulting?[/i]

It's nothing to do with an airbag per-se. It is something to do with the SRS system though. Look at the positive battery connector and there is a wire with a yellow connector coming off it. That connects the SRS ECU to the explosive charge that disconnects the battery connection in a crash.

Mine has developed an intermittent bad connection at the yellow connector. Try wiggling the two halves of the connector. Fixes mine for a while, but I think I'll need to take it apart eventually.

I wouldn't take it apart being a charged circuit I would simply replace it

I had this with mine the other week,tried to reset it with the iid tool but wouldn't clear it.
Turned out the battery voltage was on the low side,after a charge for a couple of hours and a run out it cleared itself.