How to filter noise created by 9v BMS

[itachigarra44]

So I got some of those FM transmitting modules for ghost hunting and it comes in crystal clear with a normal 9v battery. When i connect a rechargeable 9v battery it throws in a lot of back ground static and its not desirable whatsoever. Its more feasible to use the rechargeable ones sue to price and convenience. Can anyone tell me what i can add "in-line" to correct this? Preferably as low profile as possible the entire unit is no bigger than the battery box for the 9v I just attached the module with some foam and vhb tape

 

[FvM]

A battery usually doesn't generate noise. Loaded voltage and possibly impedance of the rechargeable battery may be different and affect transmitter operation. I'd measure battery voltage in operation as first step.

You are apparently assuming that the battery incorporates an electronic circuit (BMS). Any indications for this assumption? What's the battery type?

 

[Audioguru]

Maybe your FM transmitter modules use a cheap AM circuit then the FM receiver tunes to one side and uses "slope detection" of the AM adding AM interference.
Please post the FM transmitter schematic.