I have a DC-DC buck step down converter module LM2596 voltage regulator set to supply 3.0 volts to an atomic clock using a 8 Ah 12 V battery. The clock normally uses 2 AA batteries.
The battery started out at 12.07 V. After 10 days, it's at 8.45 Volts.
It does seem like it should not have dropped that much.
It claims static power: 20 ma. Does that mean power used?
The converter has a digital voltage readout. Does it use a lot of current?