Taking prompt action when you pick unusual signs on your car can help you identify and fix underlying problems before they get worse.
For example, you may notice that your car battery terminal (positive, negative, or both) is extremely hot when you touch it as you change your car’s battery or troubleshoot a car that is not able to start.
In this case, getting answers to questions such as: what causes this?
Or, how do you fix it? can help address the problem before it gets worse.
This post explains why your car battery terminals can get hot and melt, and walks you through some checks you may do to help you identify, fix and get your car battery terminal temperatures normal again.
Note: This is only intended as a guide to. Always consult a qualified car mechanic for assistance.
Quick answer: An extremely hot battery terminal (and cable) is usually a sign of a high excessive current drawn from the battery.
This high current draw is usually caused by a bad cable connection that results in a voltage drop that results in a high voltage drop.
A melted or welded battery terminal is a sign of a short circuit – with the positive cable shorting and connecting to the ground along its length.
Why your Car Battery Terminals become Hot
Your car battery terminals may become hot because of the following:
#1. Loose battery connections. A weakly connected battery terminal caused by a loose nut or bolt can result in a voltage drop along the cable connection.
This increases the current drawn and heats up both the cable and terminals.
#2. The battery cables are damaged. One of the battery cables, positive, negative, or both may have broken strands or be damaged under the insulation.
#3. Faulty battery. A faulty and shorting battery can draw high currents from the alternator heating up the terminals and in some cases damage the alternator.
#4. Faulty starter. A failing starter can also draw unusually high currents from the battery heating up the cables and terminals too.
What Checks to Do to Fix Car Battery Terminals are Hot
#1. Inspect the battery, alternator, and ground cable connections and terminals. Confirm that there is no corrosion. If there is remove it.
You may have to disconnect the cables, clean them and connect them again making sure the positive ground and alternator battery connections are clean and firmly connected.
#2. Check for voltage drops along the positive battery cable, and the ground. To check for voltage drop, measure the voltage at the start of a connection and then at the end of the connection.
Voltage drop measurements between the positive battery post and the cable terminal
Compare the two voltage readings, ideally, the voltage difference should not be more than 0.1V.
For example, to measure the voltage drop along the cable from the positive battery post to the starter motor.
Place the black (negative) probe on the negative battery post. Next, place the red (positive) probe on the positive (red) battery post and take note of the voltage reading.
Holding the negative probe in place, place the red positive probe on the battery positive terminal. The voltage reading should not differ by more than 0.1 V.
Fix: If it is higher, then there is a poor connection between the terminal and the battery post. You may need to clean the battery post and terminal or replace them with another.
Voltage drop measurements between the positive cable terminal and the positive battery terminal
Next, move the positive battery probe to the cable strands to measure the voltage drop between the battery post and the battery cable.
Check for voltage drop. It should be less than 0.1V. If higher, then there is a high likelihood of a bad cable connection, the battery terminal is not making a solid, good connection with the cable.
Fix: You may need to replace the battery terminal with another or strip down the battery cable until you get to the solid, corrosion-free wires and make another connection.
Voltage drop measurements between the positive cable battery and the car starter
Next, measure the voltage drop between the cable terminal and the starter motor. Keeping the negative probe at the negative battery post, place the red positive battery post at the starter connection.
Measure the battery voltage. A voltage drop of greater than 0.1V points to a weak or loose battery connection or damaged cable that results in heating of the cable.
Fix: If loose, tighten the cable. Replace damaged cables with another of the same gauge.
Repeat this for the cable connection to the alternator and the battery ground to chassis connection.
#3. Inspect the positive cable along its length – battery terminal to the starter, starter alternator for any signs of damage – might it be rubbing along the chassis along its length?
Are there any burn marks or discoloration? A shorting cable draws high currents that can damage it and cause the battery terminals to melt too.
#4. Could it be a faulty battery? You can use a quality digital meter to measure the battery voltage and get an indication of whether the battery is in good working condition or not.
You can also use a battery tester or take the battery for testing at an AutoZone.
At any one point, do not hesitate to get in touch with a qualified mechanic.
Should you Use a Car Battery with Melted terminals?
You should replace any damaged or melted terminals and or cables. The heat generated can damage the wire and the insulation cable increasing the risk of fire and creating a potential safety hazard.
If the battery terminals are hot or melted, it may be because of bad, loose battery connections or a shorted battery cable connection.
Check for loose battery connections or damaged battery connections. Conduct voltage drop tests along the battery cable lengths as they can point to damaged cables that need to be replaced.
Hope this helps!