Any 18v Festool battery will work with the TID 18.
And if festool are still doing it like they used to, the TID 18 will work with any Festool 'slider' style battery. So any Li-Ion or NiCad battery from 12v - 15v - 18v. . . That's backwards compatibility baby!!
Maybe [member=48572]Shane Holland[/member] is able to confirm that the TID 18 is sticking to this backwards compatibility pattern of Festool's?