@rogers1313 my systems only have the Yellow led ON when actually charging. If the battery is charged, not charginng then it is OFF. The description in “Section S”, beneath the pics https://www.envirodiy.org/mayfly/hardware/details-and-specs/ says
A yellow LED (labeled CHARGE) will light anytime the battery is being charged. Once a battery is fully charged, the yellow LED will go out, indicating that charging is done.