Replace your car's badly corroded battery cable terminals with new ones in about an hour. New terminals cost less than $20.
Corroded battery terminals can cause more problems than just poor starting. The “blooming” corrosion taking place on the battery terminals shown is a pretty extreme example. But even minor corrosion can reduce alternator output by 30 percent. That can stress your charging system and cause early failures.
On the starting side of things, the extra resistance causes slower cranking, overheated starter motor windings and premature starter failure (at about $400 each, including labor!). Prevent premature failures by replacing old corroded terminals. You just need a set of wrenches, a hacksaw and about an hour. The best part is, the whole job costs less than $20.
Unbolt the cable terminals and clean both the terminals and the battery posts
If the battery terminals have minor corrosion, just remove them and clean them and the battery posts with a wire brush. Using the wire brush, neutralize the battery acid with a baking soda/ water solution. Or buy a can of battery terminal spray cleaner. Dry off the battery with paper towels. Then apply acid neutralizing felt pads (about $3 a set) to the posts and connect the cleaned terminals (Photo 4).
Finish the job by coating each terminal with anti-corrosive spray. If the old plastic guards are damaged, install new ones (about $5 a set). But if either or both terminals don’t clamp tight or the corrosion is eating away at the metal, they should be replaced. And if you see any green corrosion on the copper cable going into the molded lead terminals, it’s a goner.
Cheap lead terminals can compromise electrical connections. A copper compression terminal offers the best connection and costs only a few bucks more.
Every auto parts store sells cheap lead battery terminals (see Photo 1). They work. But the clamp plate squashes the cable flat, so you only get partial electrical contact. Instead, get pro-style cast-copper compression terminals. A compression terminal is made from tinned copper and makes full 360-degree contact with the cable. Seal the entire connection with heat-shrink tubing to prevent corrosion. Buy QuickCable brand battery terminals at NAPA for $3 to $8 each, depending on the cable size. Also buy red and black heat-shrink tubing.
Cut the cable right where it exits the terminal. Recycle the old lead terminals—they shouldn't go in the trash.
Hold the compression nut with a wrench and rotate the terminal to compress the connection.
Reassemble the connection, using neutralizing felt pads under each terminal. Then tighten the terminal nuts and spray on a liberal coating of anti-corrosive spray.
Disconnect both battery terminals. With the battery terminals disconnected, use a slip-joint pliers to hold the terminal while you hacksaw it from the cable (Photo 2). Don’t saw it off while it’s still on the battery. Next, cut off about 1/2 in. of insulation from each cable. If the copper strands are green, clean them with a baking soda/water solution and a wire brush. Dry the cable with compressed air.
Slip the heat-shrink tubing over the cable and slide it down so it’s out of the way. Then insert the main cable and any smaller cables into the compression nut. Screw on the battery terminal and tighten until snug (Photo 3). Then slide the heat-shrink tubing over the connection and use a heat gun to shrink it.
Always wear eye protection when working on car batteries, and don’t smoke.
Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.
You'll also need a heat gun and plastic gloves.
Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.