You might have noticed that a lot of these products come with a few additional O rings. For these products to effective, it is important that no water comes in contact with the batteries. However, to charge the batteries, you need to be able to access them frequently so they cannot be sealed up completely. O rings are designed to act as a water barrier between the batteries and the plastic lid to ensure the no dirt or water breakthrough to affect the battery. Due to the fact that these O rings are made out of rubber, harsh salt water will make it break down over time. To make sure that you always keep a right seal, it’s important that you change the O ring when you notice that it is starting to break down a bit.