Aluminium alloys were tested in Al/O-2 cells with strongly acidic electrolytes containing minor amounts of chloride ions. The faradaic efficiency, the maximum discharge capacity and the peak power of various Al/O-2 cells were evaluated. The temperature dependence of the faradaic efficiency was measured for an Al/O-2 cell over the temperature range from 15 to 50 degrees C. With a zinc-containing aluminium alloy, a faradaic efficiency of 84% and a cell voltage of 1.6 V at open circuit and 0.7 V at 100 mA cm(-2) could be reached. The highest peak power 120 mW cm(-2), was obtained with an Al-Zn/Sn alloy. On the basis of the solubility of the anode products in the electrolyte, a limiting specific energy of 70 Wh kg(-1) was estimated. The cell voltage depends on the Al-alloys and on the catalyst used in the oxygen electrode. The cell voltage could be increased by about 200 mV when replacing the Pt-catalysed oxygen electrode with a noble-metal-free (CoCAA/DCD) electrode.