The T-Bird Pro-IV actually has passive humbucking pickups and a preamp. That may be whats throwing some folks off.
When did this start happening and were there any "events" prior to that, or did it just not work one day when you turned it on?
Have you opened the rear panel on the bass? If so, did you see any loose wires inside?
Since you've tried multiple cables, and amps, plus replacing the battery, that seems the most logical choice.
Do you have any other instruments you can try with the amps to verify they are working normally with them?
If you can take pictures of the electronics in the rear panel, that will help as well.
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