The invention relates to an aldehyde conversion method comprising putting an aldehyde into contact with oxygenated water and with a catalyst, under oxidation conditions, wherein the catalyst is a molecular sieve with pores of a diameter of at least 0. The controller acquires the temperature of the nickel metal hydride battery when the nickel metal hydride battery is being charged or discharged and the temperature of the nickel metal hydride battery when the nickel metal hydride battery is not being charged or discharged with the use of the temperature sensor. The audio apparatus further includes a speaker coupled to the sound module, in various embodiments.