If you have a 2 volt battery and need to use it to power glow plugs, using a 1.5 volt plug can be dangerous. Connecting the battery directly to the plug can cause overheating and damage the plug or other components. To reduce the voltage to a safe level, you will need to use an appropriate voltage reduction circuit such as a voltage regulator or voltage divider. These devices will help reduce the voltage to the correct level without the risk of damaging the equipment.