The contribution of synthetic fibres to the puncture resistance of absorptive glass-mat (AGM) battery separators when they are combined with glass microfibres is presented. Other mechanical characteristics necessary for the automated manufacture of batteries are also improved by the addition of well-chosen synthetic fibres. The selection of these synthetic fibres is of paramount importance given that specific physical parameters such as wicking, porosity or wettability have to be taken into account to design a useful and long-life AGM battery separator.