I did a search on the forum for this question but could not find the answer. I am sure it is out there. So here is my question. If you measure the battery voltage topside at what voltage would you want to start thinking about replacing the batteries? I have played mine around 25 hours and still have close to 36 volts across the 9v string and 3v across the D cells. I know I am not close to thinking about changing them but thought it an interesting question.