Springers Solar guide to 12V electrics: Solar regulators

Solar Regulators: Putting Sunlight into Your Batteries. And how to make sure that your panels don’t draw it back out.
Solar panels are great for collecting energy from the sun but they need a solar controller to ensure the correct amount of energy is going to your batteries. If batteries are overcharged, they will at the least be damaged so they will have a reduced battery life. At worst, they will be damaged to the point of being unusable.