inside the commodore sr-9190r

 shown here the connections on the board for the battery and external psu.

normally, the batteries are sealed inside the unit as three AA nickel cadmium cells. these are recharged when the external 9v psu is connected.

normally, the rechargeable cells are dead, and possibly leaking. you can remove these cells and make up a new battery pack. if you do, it is advisable to use nickel cadmium rather than metal hydride if you plan to use the original charger.

an alternative is to remove the cells altogether and just use the external psu. this is what ive done. but beware, if you do this, do not use the original 9v psu because the cells act as a load when connected. without the cells use a lower voltage. i found 5 volts to be fine.

also, the mini jack power plug requires +ve tip.