The type of demand that exist between torchlight and battery is

The type of demand that exists between a torchlight and a battery is complementary demand. This is because the demand for torchlight and batteries are related to each other, and one product (the battery) is needed to use the other product (the torchlight). In other words, the demand for batteries is directly related to the demand for torchlights, and vice versa. If there is an increase in demand for torchlights, there will likely be a corresponding increase in demand for batteries to power those torchlights. Similarly, if there is a decrease in demand for batteries, there will likely be a decrease in demand for torchlights, as they will not be able to function without a power source. Therefore, torchlights and batteries are considered complementary goods that are often used together.