Requirements for Battery Terminal Coversby Richard Rowe
While battery terminal covers aren't strictly necessary, many new vehicles use them to prevent short-circuiting or arcing against the car body. Battery terminal covers can be plastic, rubber or any kind of synthetic polymer that can seal the terminals against water and incidental electrical contact.
The battery terminal cover's primary task is to protect against accidental contact by metal components or unwary mechanics. The negative battery terminal is grounded to the body, so accidental contact will not generally result in an electrical reaction. The positive terminal is another matter; if you complete a circuit with the positive terminal, potentially deadly current will flow through the metal tool, hand or forearm that bridged the gap. This can be especially crucial for newer cars, which may have very little clearance between the terminal and the hood, which is near enough that under certain conditions, the battery may arc to the underside of the hood, burning the paint off and damaging the battery.
Sealing and Corrosion Resistance
Although the lead battery posts and brass terminals are fairly resistant to normal moisture-induced corrosion, they're not immune to it. Lead easily dissolves in the presence of nitric acid, which is a component of acid rain and results from a combination of vehicle and industrial emissions. Normal atmosphere always contains a little bit of nitric oxide, which turns into nitric acid when it mixes with water. Battery terminal covers are critical for keeping the terminals free of water, which may convert to nitric acid and corrode the lead battery post if the car happens to be in a high-smog environment. A battery terminal cover doesn't need to completely seal the terminal; keeping water off will suffice to prevent corrosion.
Almost all batteries produce hydrogen while recharging, which can be a serious problem, since many vehicles incorporate the battery as a link in the electrical system. Such vehicles are always pulling power from the battery, so the alternator must constantly recharge it. Hydrogen gas buildup isn't normally a problem, but explosions are possible. Battery terminal covers prevent arcing and deny the gas a source of ignition, making electrical insulation doubly important.
If you've ever had to jump-start a car in the dark, then you know how difficult it can be to identify the positive and negative terminals if they aren't color-coded. While the battery itself will carry a stamping or sticker to indicate the positive and negative terminals, these will do little good in the dark. Bright red or yellow positive battery terminal covers are far more apparent in low light conditions than any marking on the battery itself, and help to prevent a possibly expensive mistake.
- dead battery image by Katrina Miller from Fotolia.com