Small electromechanical relays are not good for switching low levels of voltages and currents. Electromechanical relays need a hefty voltage and/or current to break any film buildup. It is this film buildup that won’t allow very low voltages and currents to pass through the contacts. Reed switches are clearly the best. Using sputtered ruthenium contacts or iridium contacts are the best materials for these low level loads.