TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - The electrolyte is preferably an aqueous 1-13 mol/l sodium or potassium hydroxide solution. The anode paste preferably comprises (per 100 pts.wt. metal powder) 16-50 pts.wt. deionized water, 13-44 pts.wt. KOH or NaOH, 0.5-6 pts.wt. gelling agent and up to 20 (especially 6.5-20) pts.wt. additive(s) selected from conductivity improvers (e.g. graphite powder), solid lubricants (e.g. graphite powder or PTFE powder), dispersing agents (e.g. zinc oxide) and electrochemical reaction promoters (e.g. cellulose for regulating the water content in the liquid phase). The cathode collector (6a) preferably consists of a porous foil including a water-repellant porous layer bonded to a porous conductive layer which consists of sintered metal or carbon powder optionally containing a binder and an oxygen reduction catalyst and which acts as a separator between the electrolyte and an air film.    TECHNOLOGY FOCUS - METALLURGY - The anode metal powder preferably comprises aluminum, iron, cadmium, lithium, magnesium, lead or especially zinc powder of 0.01-100 microns particle size.    TECHNOLOGY FOCUS - POLYMERS - The anode paste preferably contains a low friction coefficient additive, which may be a fluorine-containing polymer such as PTFE powder, and a gelling agent such as carboxymethyl cellulose or a polyacrylate. The cathode collector (6a) preferably has a water-repellant porous layer e.g. of sintered fine PTFE grains. EXAMPLE - In the battery (1) shown in the drawing, each cell had a 1.5 V open circuit voltage and a thickness of 0.5 cm, the paste strip (4) being 0.3 cm thick. For a 6 V battery, the thickness was 2.5 cm excluding the outer casing, the latter having a height of 20 cm and a width of 6 cm. The paste (4) had the composition 100 pts.wt. zinc powder (10 microns average particle size), 45 pts.wt. water, 38 pts.wt. KOH, 2 parts gelling agent and 12 pts.wt. additives, had a viscosity of 3 Pa.s. and was passed through each cell at 0.6 mm/min. The battery had a usable energy density of 230 Wh/kg battery (or 550 Wh/l battery) and a power density of 20-100 mW/cm2. These results were reproducible over several discharge/charge cycles.