Doubling voltage of two 9V batteries in series? [OR high voltage]

Using Arduino Project Guidance
3

You could use a circuit called a charge pump:

The References section of the above link has some good links to additional information.

For lower voltages, devices like the TC7660 can be used to double 5V to 10V, for example, but 36V is too high for all the devices I know of. You may have to build it out of discrete components.

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