Let me be very specific- I am looking for the actual criteria as to when the "traction" battery needs replacing in a hybrid. My wife's Camry hybrid hardly ever runs off just the battery. The gas engine is off at a stop light or going down hill but almost all the rest of the time the gas motor is running. It seems at very slow speeds and for very short distances it should run off the battery. How does one tell when the traction battery needs to be replaced? There should be a quantitative description, not just "it depends" Thanks!