I want to use a 7.2V (4200mAh) battery with my raspberry pi but I need to convert the output to 5V (2000mAh), I tried the following formula:
Ω = V / A
but when I try to find the ohms the result is 0.78
|7.2/4.2 - 5/2| = 0.78
How can I find the correct ohm (to use a resistor) to get an output of 5V and 2A?