Using an insulating grease on electrically mating parts seems to be a contradiction. The stuff insulates. So why do people recommend putting it between conductive surfaces and expect minimal resistance between the parts? I was suspicious for years. I would not use it. For a while I coated the outsides of battery connections after they were complete, but that was pretty messy. Dielectric grease tends to get tracked around when someone touches it. It’s difficult to remove completely and nothing (repeat: nothing) will stick to a surface contaminated by a film of silicone dielectric grease.
My problem was thinking of the stuff in the same category as high-pressure grease. High-pressure grease has a high mechanical film strength to keep parts separated even when they’re not moving. Dielectric grease has essentially no mechanical film strength. When pressing parts together, it readily flows out of the way, allowing metal to metal contact. (it can get trapped between two rough surfaces where it insulates. It essentially cuts down the contact surface area.) Usually a silicone compound, dielectric grease resists air, water, oil, acids and solvents. It seals a connection and prevents oxidation or corrosion.
By all means coat those battery terminals after brushing them bright. Then attach clamps and cables. The grease will flow out of the way and allow a good mechanical connection to be a good electrical connection. The tracking problem can be mitigated by using the compound sparingly.
Dielectric grease is appropriate for electrical connectors exposed to water. I never count on it to make things waterproof by itself. Being transparent, its too easy to miss a spot. Having such little viscosity and film strength, it’s too easy to brush off. Its better inside mating parts. The substance is particularly good for RF coax connectors. Silicone grease has the same dielectric properties as air, namely a dielectric constant of 1, so coax connectors can be filled with the stuff and it doesn’t change their transmission properties.
As long as water cannot get at the connecting surfaces, corrosion cannot occur. Again: corrosion CANNOT occur in the absence of water molecules, but that’s another story.
I wrote a few things about keeping battery terminals clean and dry before I figured out the wonder of dielectric grease.
Dielectric grease makes a wonderful sealant to use every time you thread a stainless fastener into aluminum. It keeps water out and you will be able to unscrew the parts years later.
added 5/30/06