I am trying to get a 5V output out of a 2S 18650 cells (getting a 7.5V from them.)
I am trying to use a LM2596 module, but as soon as the battery is connected to the LM2596, the input reading goes down to 2.5V. The LM2596 does not work with this voltage as expected. I also tried using an Arduino 5V as the input to the LM2596 and it works as expected, bringing the voltage down. This is being tested without any load at the output as I have to first regulate it.
Why does this happen with the 18650 batteries?