I am trying to power an Arduino Uno as well as my circuit using Li-Ion batteries. They are 2 18650 Lithium Ion batteries (rated at 3.4 V each = 7.4 V total).
I have this battery plugged into the Vin pin of the Arduino and in parallel is the circuit I am powering. The circuit requires approximately 450 mA.
The issue is, when I have everything actually hooked up I only get power going to the Arduino. The remaining circuit can pull a max of maybe 15 mA. When I use a regulated power supply (such as a programmable power supply) to power the Arduino, and the batteries to power the circuit, everything works just as intended. The issue arises when I try to power both Arduino and circuit with just the Li-Ion batteries.
Also worth noting is that the input of the circuit I'm trying to power is a 5 V voltage regulator. But it is rated up to 1.5 A; much more than my circuit needs.
Where am I going wrong?