ADC still only goes down to 12 even when battery-powered and other breadboard disconnected (3 new alcaline 1.5V).

Vref- of 15mV still connected.




I always thought battery-power was essentially noise-free (in a "clean" environment); either a straight line going up when charged, or slowly down when powering a circuit, or even much slower down over time when disconnected.

I don't get it.