Roland TR-808 Bass Drum Breadboard Project

2 Batteries will work just fine and will not hurt anything in your circuit but as they loose charge the voltage will drop and maybe make it sound a bit different ie drop in volume or some minor thing. At some point the voltage of your batteries will droip below (3 or 4 volts) the minimum voltage for some component. I think op amps like TL072 work right down to 3 or 4V then they just stop working (ie you will hear no sounds) at which point you just replace the batteries! This method will work for any circuit that requires a split supply. Of course you could use 2 x 12V batteries but they are not so common unless you use 2 car batteries or something crazy! I have used both methods to test modules (2 x 12V car batteries and also 2 x 9V square batteries. However, it is quite easy to find an old 24VDC wall wart in your attic and use a resistor divider to make a virtual ground then 2 big caps for smoothing.
This page shows the various methods described above:
https://tangentsoft.net/elec/vgrounds.html
Kevin.