Most 4s stores use internal resistance measuring instruments to test the health of batteries. The detection accuracy of this instrument is above 95%, because the health of the battery is directly related to the internal resistance of the battery.
Generally speaking, the battery voltage is around 12V, but after the car starts, the voltage will rise to around 13- 14V, which is basically a normal voltage value. If the starting voltage of the car is found to be lower than 12V or 13V, it means that the battery loss is relatively large and can be replaced.