Float charging a battery comprises charging a battery to a reference voltage that is less than a maximum voltage of the battery. A power source provides power to a charging circuit. The circuit supplies a reference voltage. An operational amplifier float charges the battery to the reference voltage. A comparator determines whether the battery's voltage exceeds the reference voltage. Another comparator determines whether current through the battery exceeds a reference current. A thermistor determines whether the battery's temperature exceeds a safe range. A microprocessor monitors the inputs from the comparators and the thermistor and outputs of the circuit. If the comparators or the thermistor reports a safety fault to the microprocessor, the microprocessor shuts down the charging current to the battery. If an output circuit draws too much current from the battery, the microprocessor can disconnect the battery from the output circuit.