Abstract: A method for evaluating the condition of a battery comprises coupling a first power transistor as or as part of a first external load in series with the battery, coupling a second power transistor as or as part of a second external load in series with the battery, and conducting each power transistor to draw a transient large current from the battery while sampling the voltage across the battery and voltage across the load, from which the internal resistance of the battery can be determined. The internal resistance of the battery can then be compared with a predetermined nominal value to issue a warning if the battery is weak. The invention enables, for example, a driver to correctly know the actual condition of an automobile battery in substantially real time while consuming a minimum amount of power.

Abstract: The method comprises coupling an external load having a predetermined resistance directly in series with the battery, conducting a power transistor to supply a transient large current to the battery for sampling voltage of the battery in a set very short period of time, and determining the internal resistance of the battery. The internal resistance of the battery can then be compared with a predetermined warning value of internal resistance of the battery so as to determine whether the former is equal to or larger than the warning value, and displaying a warning on a display if the determination is affirmative. The invention enables a driver to correctly know the condition of the battery in substantially real time while consuming a minimum amount of current.

Abstract: A method and a device for monitoring a motor vehicle's electric power, in which the method comprises the steps of sampling, calculating, comparing, displaying results, and counting intervals, and the device comprises a stabilizing circuit, a CPU, a voltage sampling circuit, a current control circuit, and a color lamp display circuit. The step of sampling is performed when the load and power transistor are enabled (i.e., there is a great amount of current) and with a very short sampling time so that the invention can inform a driver about a status of a battery by consuming very little power.