Once a year (or as necessary), the battery terminals and the cable clamps should be cleaned. Loosen the clamps and remove the cables, negative cable first. On batteries with posts on top, the use of a puller specially made for this purpose is recommended. These are inexpensive and available in most auto parts stores. Side terminal battery cables are secured with a small bolt.
Clean the cable clamps and the battery terminal with a wire brush, until all corrosion, grease, etc., is removed and the metal is shiny. It is especially important to clean the inside of the clamp thoroughly (an old knife is useful here), since a small deposit of foreign material or oxidation there will prevent a sound electrical connection and inhibit either starting or charging. Special tools are available for cleaning these parts, one type for conventional top post batteries and another type for side terminal batteries. It is also a good idea to apply some dielectric grease or petroleum jelly to the terminal, as this will aid in the prevention of corrosion.
After the clamps and terminals are clean, reinstall the cables, negative cable last; do NOT hammer the clamps onto battery posts. Tighten the clamps securely, but do NOT distort them. Give the clamps and terminals a thin external coating of grease after installation, to retard corrosion.
Check the cables at the same time that the terminals are cleaned. If the cable insulation is cracked or broken, or if the ends are frayed, the cable should be replaced with a new cable of the same length and gauge. Note that battery cables can corrode beneath the insulation which may be hard to detect. The result may be an open circuit, poor starter operation, as well as other battery problems. Replacement of the cable(s) is the only solution.
Disconnecting The Cables
When working on any electrical component on the vehicle, it is always a good idea to disconnect the negative (-) battery cable (some diesel-engine vehicles have two batteries, and therefore two cables which must be disconnected). This will prevent potential damage to many sensitive electrical components such as the Powertrain Control Module (PCM), radio, alternator, etc.
Before you disconnect the cable(s), first turn the ignition to the OFF position. This will prevent a draw on the battery, which could cause arcing (electricity trying to ground itself to the body of a vehicle, just like a spark plug jumping the gap) and, of course, damaging some components such as the alternator diodes.
When the battery cable(s) are reconnected (negative cable last), be sure to check that your lights, windshield wipers and other electrically operated safety components are all working correctly. If your vehicle contains an Electronically Tuned Radio (ETR), don't forget to also reset your radio stations. Ditto for the clock.
Anytime the battery cables have been disconnected and then reconnected, some abnormal drive symptoms could occur. This is due to the PCM losing the memory voltage and its learned adaptive strategy. The vehicle will need to be driven for 10 miles (16 km) or more until the PCM relearns its adaptive strategy, and acclimates the engine and transmission functions to your driving style.