Picky bass problems

I bought an cheap ass bass few months back from my friend who doesn't know anything about basses.

Today i was making a new song and suddenly the volume from the bass started to fade. Found out that my bass was an active electronic bass and the 9v battery had runned out :D

Called to my friend that did she even know
That her old bass had active electronics. Yep she didnt even know. That being said i knew that the battery had to be about 6 years old :D wtf