1. A battery service system comprising: connectors configured to couple to a battery; a signal source coupled to the connectors for generating signals with time variant components configured to apply the signals to the battery continuously during a battery test; a processor coupled to the connectors and configured to receive signals representing a battery response to the applied signals, and to generate a battery parameter based on the battery response to the applied signals with time variant components; and an output device for generating an output representing the battery parameter.