A respiratory system and method includes a filling unit for filling a portable bottle of respiratory gas and a conserver for mounting on such a bottle. A battery on the conserver may be recharged when the bottle is placed on the filing unit. The conserver may include electric timing circuitry operative to control the timing of pulsed flow of respiratory gas from the conserver, and an external electrical coupler to enable adjustment of the timing of the pulsed flow. The conserver may include at least one sensor operative to sense the reversal of flow between exhalation and inhalation, the conserver being operative to commence a respiratory gas delivery pulse in response to the sensing of the reversal of flow.