A single cell AA lithium likely already has a 3.7v (IIRC) to 1.5v step down, but also likely has a cut-off voltage to protect the internal cell too.
If it's built-in lithium then you're as likely put in a step-down or a buck-boost to regulate raw lithium cell pack voltages to whatever the device needs internally, but that also needs a self-protection cutoff.
If it's built-in lithium then you're as likely put in a step-down or a buck-boost to regulate raw lithium cell pack voltages to whatever the device needs internally, but that also needs a self-protection cutoff.