A system and method for secure charging of a motor vehicle battery including the steps of secure charging of the battery of a motor vehicle from a network estimating the resistance between the earth and the neutral of the network, including at least one injection of pulses of current into the network, measurements of voltage between the earth and the neutral of the network in response to each pulse, and a determination of the earth resistance from the measured voltages. Each injection of current pulses into the network includes the injection of a first positive pulse followed by a second negative pulse, the first and the second pulses having an equal intensity in terms of absolute value and being separated by a sufficiently short interval for a stray capacitor coupled to the network to be further charged during the second pulse.