I have an item that I'm trying to increase its speed slightly as well as its play duration. It typically takes 3 C cell batteries, which causes it to be very slow and may last an hour. I wired a 9 volt battery in but it's too fast; however, the duration has increased.
What I would like to do is wire in two 9 volt batteries but limit the out going voltage to about 6 or 6.5 volts. I'm just not sure what level resistor to use or if there's a online calculator that would help.