1. Use the multimeter to measure the virtual voltage of the battery. Whether the battery is turned on or not can be known by charging the battery. If the internal resistance of the battery is large or there is a broken grid, the current will be small. If the current is normal but the voltage is low (for example, below 12V and cannot be charged), there may be a short circuit.
2. It is very meaningful to measure the battery voltage while loading the battery.
For example: connect a 12V100W bulb and measure the battery voltage at the same time. If it is above 12V, it is normal. If the light is very bright at first, it gradually darkens, that is, the battery is dead and needs to be recharged.
If the light is on but the voltage is only about 9V and can last, it means there is a short circuit. If the load voltage is 0, it means that the internal resistance of the battery is very large or there is a broken grid.
The internal resistance of the battery is generally caused by severe vulcanization.