Hello, I'm having trouble hooking up my Arduino nano to an external power supply.
When I connect it via USB, it works fine as my LED will turn on so there is nothing wrong with the sketch. The LED is just supposed to turn on, that's it. The problem is how I hooked up my battery to the nano as the LED will not turn on. There is power going to the nano as the little power light on the nano is on and the two 18650 batteries are fully charged. I don't know where I went wrong connecting the battery to the nano. Help?
How are the "two 18650 batteries" connected? Series or parallel?
Your diagram doesn't show any connection between battery - and Arduino GND unless dots have some meaning that I don't understand.
Steve
I will make a voltage tester to see what the reading is on the 5V.
Sorry, the dots are the rails on the breadboard.
Two 18650 batteries in parallel will give 3.7V which is at the edge to run a 328P at 16 MHz.
Two 18650 batteries in series will give 7.4V which is too much for the 328P on the 5V pin.
Hi,
OPs circuit and edited.
Tom.. 
