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Accurate state-of-charge (SOC) estimation in lead-acid batteries is an ever-increasing necessity in an industry that demands low-maintenance costs and highly available systems. If the batteries are charged by photovoltaic panels and are installed in remote sites and exposed to aggressive environmental conditions, the problem of extending the batteries' useful life becomes a challenge. Modern charge-controllers can do a very good job extending the batteries' life, but any charge-controller is as good as the measurements taken to feed the control algorithm. Estimating SOC in lead-acid batteries is generally acknowledged as a difficult problem. This paper presents a method to estimate SOC by means of an artificial neural network First, the network is trained using precise measurements of voltage, current and temperature under different charge-regimes. Ampere-counting (A-C) is used during training to determine SOC. Once the training is completed, the neural network can accurately estimate SOC using precise measurements of voltage and temperature and rough measurements of current. This method has the advantage of requiring no precise current measurements. Accurate current measurements tend to increase the cost of the controller. The resulting neural network has been implemented in a microcontroller-based charge-controller.