A battery condition monitor is described that can be integrally mounted within a valve-regulated lead-acid (VRLA) battery. The device continuously monitors battery voltage, temperature and elapsed time. These parameters are processed to identify the status of the battery in terms of charge, discharge or resting modes. The state-of-charge is determined based on voltage and temperature measurements taken during resting periods, when the battery components adequately approach equilibrium conditions. The resulting whole-life record, built from the integration of instantaneous readings, is compared with a simple life model, based on the number and the depth of the discharges performed. Laboratory tests and ongoing field trials indicate that this approach can provide cost-effective and convenient monitoring of VRLA batteries in specific types of application. (c) 2004 Elsevier B.V. All rights reserved.