There's a device in your active bass that has three parts, an anode (-), a cathode (+), and the electrolyte.
The chemical reactions in this device causes a build up of electrons at the anode. This results in an electrical difference between the anode and the cathode. You can think of this difference as an unstable build-up of the electrons. The electrons wants to rearrange themselves to get rid of this difference. But they do this in a certain way. Electrons repel each other and try to go to a place with fewer electrons.
In this divice, the only place to go is to the cathode. But, the electrolyte keeps the electrons from going straight from the anode to the cathode within it. When the circuit is closed (a wire connects the cathode and the anode, such as activating the electroncs in your bass) the electrons will be able to get to the cathode by going through the active electronics.
However, these electrochemical processes change the chemicals in anode and cathode to make them stop supplying electrons. So there is a limited amount of power available from this device.
OEM replacement device are, of course, highly desirable, however a number of third party manufacturers also make suitable substitutions.
All kidding aside, it's most likely that (the battery) or your clipping the input on your amp or processor.