"The battery is new, but the starter turns weakly."
"There's white powder on the terminals."
"The condition changed after re-tightening the battery terminals."
In such cases, the possible cause is:
"Contact resistance."
In automobiles, large currents flow from the battery to the starter motor and various electrical components.
Even if the battery itself is normal, problems can arise if:
Terminals are loose.
Contact surfaces are corroded.
Cable terminals are in poor condition.
Connecting parts are dirty.
Such conditions can create extra resistance in the path of electrical flow.
Even a slight resistance in places where large currents flow can lead to:
Voltage drop.
Heat generation.
Worsened starting performance.
Instability of electrical components.
This article will explain in an easy-to-understand manner what battery terminal contact resistance is, why the condition of the terminals is important, and how to address corrosion and looseness.
What is Contact Resistance?
Contact resistance is:
Electrical resistance that occurs at the point where metals come into contact.
For example:
Battery terminals.
Cable terminals.
Bolts and nuts.
Grounding points.
Connectors.
Relay contacts.
All have contact surfaces where components connect to allow electricity to flow.
Ideally, metals would be in complete close contact, allowing electricity to flow without resistance.
However, actual metal surfaces have:
Microscopic irregularities.
Oxide films.
Dirt.
Corrosion.
Oil.
As a result, even if they appear to be in contact over a large area, electrically they may only be contacting in limited spots.
The resistance generated at these connection points is contact resistance.
Panasonic also describes contact resistance as resistance present at the contact points between contacts and terminals, and measures it using the voltage drop method.
Why is Contact Resistance Important for Battery Terminals?
Large currents flow around automotive batteries.
The starter motor, in particular, requires a very large current when starting the engine.
In such areas, even a:
Very slight resistance
can have a significant impact.
For example, if there is extra resistance in the electrical path of:
Battery.
Terminal.
Cable.
Starter.
Ground cable.
Then voltage will be lost at that point.
This can lead to a situation where:
The battery has sufficient voltage,
but not enough voltage reaches the starter.
What is Voltage Drop?
In an electrical circuit,
Voltage drop occurs when current flows through a resistive component.
The basic relationship is:
Voltage = Current × Resistance
This means that even with the same resistance,
The greater the current flowing, the greater the voltage drop.
Suppose there is a resistance of:
0.01Ω
at the connection point.
If 100A flows through it, there will be a voltage drop of:
100A × 0.01Ω = 1V
For a 12V automotive system, a 1V drop is not insignificant.
Moreover, actual starters can sometimes draw currents well over 100A.
Therefore,
Even very small contact resistance values can cause problems in high-current circuits.
Contact Resistance Can Also Cause Heat Generation
When current flows through a resistive component, heat is also generated.
Especially in battery terminals, where large currents flow,
Loose terminals,
Corrosion of contact surfaces,
Insufficient contact,
etc. can increase resistance and cause the connection point to overheat.
GS Yuasa also warns that:
If battery terminals are loose, not only does starting performance worsen, but that part can become a source of contact resistance and generate heat, which is dangerous.
This means that the fastening condition of the terminals
is not simply a matter of "as long as they don't come off."
It is necessary to maintain good electrical contact.
What Happens if Battery Terminals Are Loose?
If terminals are not sufficiently secured, problems can arise such as:
Reduced contact area.
Changes in contact condition due to vibration.
Potential for minute discharges at the contact points.
Increased likelihood of oxidation and corrosion.
As a result, symptoms may include:
Weak starter turns.
Only a clicking sound when starting the engine.
Electrical components momentarily cutting out.
Unstable headlight brightness.
However, these symptoms can also be caused by battery life, starter failure, or alternator malfunction.
The symptoms alone cannot definitively determine that the terminals are the cause.
What is the White Powder?
Around battery terminals, you may see:
White powder.
Bluish-white powder.
Verdigris-like deposits.
This indicates that corrosion may be progressing around the terminals or posts.
Panasonic also states that if white powder repeatedly appears on the terminals, or if the battery terminals or cable terminals are corroded, it can lead to poor contact.
GS Yuasa also lists corrosion and rust on terminals and cables as inspection items.
A small amount of deposits does not immediately mean a serious malfunction, but if:
It repeatedly appears.
Corrosion is spreading.
The terminals are deformed.
The cables are also damaged.
Then it would be wise to have it inspected.
Why Does Corrosion Impede Electrical Flow?
When oxides or corrosion products form on metal surfaces,
they can hinder good metal-to-metal contact.
In other words, it's as if a layer that doesn't conduct electricity well is inserted between:
The metal of the battery terminal,
and the metal of the cable terminal.
This increases contact resistance, leading to a larger voltage drop when the same current flows.
Therefore, terminal corrosion is not just a:
Cosmetic issue.
It also affects the performance of the electrical circuit.
Is Tighter Always Better?
No.
While terminals shouldn't be loose,
Tighter is not always better.
Battery terminals can be made of relatively soft metal, and applying excessive force can:
Deform the terminals.
Damage the terminal posts.
Stress the battery itself.
GS Yuasa also warns that overtightening can damage the terminals.
Panasonic also states that excessive tightening can put a strain on the terminals and lead to corrosion.
The basic principle is to:
Follow the methods and tightening specifications designated by the vehicle or battery manufacturer.
Will Expanding the Contact Area Reduce Resistance to Zero?
Contact area is important, but it's not the only factor.
The electrical contact condition is also influenced by:
Surface material.
Surface oxidation.
Roughness.
Pressure.
Dirt.
Fastening method.
Temperature.
Vibration.
Even if there appears to be good contact, if there is an oxide film on the metal surface, it may not be in an ideal state.
Conversely, if proper metal contact is achieved with an appropriate terminal shape and tightening force, very low resistance can be achieved.
Is Cleaning Battery Terminals Effective?
If corrosion or dirt is present, proper cleaning can potentially improve the contact condition.
GS Yuasa suggests:
Cleaning corrosion or rust with sandpaper or a wire brush and applying a thin layer of anti-corrosion grease.
They also explain that even when replacing a battery, if there is corrosion on the cable terminals, poor contact can result if they are not cleaned.
However, cleaning requires caution.
There is a risk of sparks or short circuits around the battery.
If you are unsure of the procedure, it is safer to ask a car dealership or repair shop.
Why is a Short Circuit Around Battery Terminals Dangerous?
Automotive batteries can supply large currents.
For example, if a tool simultaneously touches:
The positive terminal,
and the vehicle's metal body,
a very large short-circuit current can flow.
This can lead to dangers such as:
Sparks.
Overheating of the tool.
Component damage.
Fire.
Ignition of gases produced by the battery.
GS Yuasa also warns that short circuits caused by positive/negative terminals or metal tools can lead to fire or ignition.
Therefore,
"Just cleaning the terminals a bit"
must be treated as electrical system work.
The Order of Disconnecting Battery Terminals is Also Important
For a typical 12V vehicle, when disconnecting the battery,
the negative terminal first,
then the positive terminal,
is generally the recommended order. The reverse is true for connecting.
This is because the entire vehicle body is used as the negative electrical path.
By disconnecting the negative side first, the risk of a short circuit if a tool touches the vehicle body is reduced.
However, in modern vehicles, various factors may be involved, such as:
Battery current sensors.
Backup power.
ECU learning.
Idling stop systems.
Security systems.
Please check the owner's manual or service manual for your specific vehicle.
Can a Tester Determine the Terminal Condition by Measuring Voltage?
Simply measuring the terminal voltage of the battery alone
does not completely reveal the state of contact resistance.
For example, while the engine is off,
a normal voltage of 12.6V may be present,
but a large voltage drop could occur at the contact points the moment the starter is engaged.
This is because the effects of contact resistance tend to appear
when a large current flows.
Therefore, in maintenance,
"voltage drop measurement," where the voltage across both ends of a connection is measured under load,
is used. The use of the voltage drop method for measuring contact resistance is also shown in Panasonic's technical documentation.
Is it the Battery or the Terminals?
This is extremely important.
If engine starting performance is poor, there could be multiple causes, such as:
Degradation of the battery itself.
Poor contact at the terminals.
Ground cable issues.
Starter motor problems.
Charging system issues.
For example, Panasonic lists the possibilities of:
Internal battery degradation,
Insufficient charging,
Or issues with vehicle-side charging devices like the alternator or regulator,
if the voltage drops quickly even after charging.
Therefore,
"A weak starter means replacing the terminals will fix it"
is not always true.
It is necessary to isolate the cause.
Even a New Battery Cannot Perform Well if the Terminals are Bad
Even if a new battery is installed, if:
The cable terminals are corroded,
The fastening is insufficient,
Or there's a problem with the ground cable,
then the electrical path cannot be considered good.
In other words,
Battery performance
and the
connection condition for transmitting electricity from the battery to the vehicle
are separate.
When replacing a battery, it is advisable to check:
The terminals,
Cables,
Fastening condition,
And surrounding corrosion.
How Does Contact Resistance Differ from Grounding?
Article 17 explained:
Vehicle grounding.
Grounding primarily deals with the electrical paths of:
The negative side of the battery,
Engine,
And body.
This article on contact resistance focuses on:
"The quality of the connection points" within those electrical paths.
For example, even if a thick ground cable is installed, if:
The terminal part is corroded,
The bolt is loose,
Or the contact surface is not appropriate,
then the resistance at the connection point can become an issue.
This means that not only
using good cables
is important, but also
creating good connections.
Does the Material of Battery Terminals Make a Difference?
Different metals have different electrical resistances.
Copper and silver are known for their high conductivity.
Therefore, in electrical wiring and contacts, material and surface treatment are important design factors.
However, the actual terminal performance is not solely determined by:
The material alone.
Contact pressure,
Surface treatment,
Corrosion resistance,
Mechanical strength,
Fastening method,
Temperature,
And environmental conditions also play a role.
Therefore,
it cannot be simply concluded that "a certain metal will always be effective."
What is the Purpose of Plating?
In electrical contacts, plating may be used for purposes such as:
Conductivity,
Corrosion resistance,
And contact stability.
For example, silver is one of the materials used in electrical contacts due to its high conductivity.
However, the performance of plating varies depending on:
Thickness,
Base material,
Surface condition,
Applied load,
Wear,
And environment.
Repeated tightening and loosening can also damage the surface treatment.
Therefore, for plated terminals and bolts, it is important to follow the specified usage instructions.
Next Science's Battery Terminal Products
Next Science offers a "Battery Terminal Screw Set" as one of its products focused on the electronic environment.
The official page states that the automotive M6 type uses oxygen-free copper with silver plating.
However, this product also has specific usage conditions.
The official page advises:
To use it on the negative terminal.
Not to use it on the positive terminal.
To follow the specified tightening conditions.
In other words, terminal components
should not be judged by material alone.
They must be used correctly, including the installation location and fastening method.
Next Science's Approach to Electronic Environment
Next Science positions the
electronic environment
as one of its technology research areas.
When examining automotive electricity, there are multiple factors to consider, not just:
Voltage,
Current,
And wiring,
but also:
Contacts,
Contact resistance,
Materials,
Static electricity,
And potential difference.
Next Science's Technology page also treats the electronic environment as an independent technological domain.
Battery terminals are small components, but they are:
Crucial connection points that send electricity to the vehicle.
That's why it's important to not just look at large components, but also to consider:
"Where the electricity flows and where it makes contact."
5 Key Points to Check on Battery Terminals
When inspecting around the battery, check the following points:
First, are the terminals loose?
Second, is there white powder or corrosion?
Third, are the cables or terminals damaged?
Fourth, is the battery itself properly secured?
Fifth, is there any abnormal voltage drop during starting or under load?
However, modern vehicles may have sensors or other devices installed around the battery.
Do not add or modify wiring on your own; consult the owner's manual.
If You Experience These Symptoms, Have Them Inspected
If you experience any of the following symptoms, consider having your power system, including battery terminals, inspected:
Unstable engine starting.
Weak starter.
Symptoms do not change even after replacing the battery.
Terminals become abnormally hot.
Severe corrosion on terminals.
Electrical components intermittently cut out.
Burning smell.
Discoloration of terminals or cables.
Especially if there is:
Abnormal heat generation,
Smoke,
Burning smell,
Or sparks,
do not continue using the vehicle and consult a specialist.
Summary: Not Just Battery Performance, But "Connection Points" Are Also Important
Battery terminal contact resistance refers to:
The electrical resistance that occurs at the connection points between metals, such as battery terminals and cable terminals.
Even if contact resistance is a very small value,
in places where large currents flow, such as starter motors, it can lead to:
Voltage drop,
Heat generation,
And reduced starting performance.
The main causes of increased contact resistance include:
Loose terminals,
Corrosion,
Oxidation,
Dirt,
Condition of contact surfaces,
And deterioration of cables or terminals.
What's important is not just
"what voltage the battery has,"
but how stably that electricity flows through:
The terminals,
Cables,
Ground,
And various electrical components to the vehicle.
And for maintenance, it's not simply a matter of:
Tightening it as much as possible,
Polishing it,
Or replacing it with expensive terminals.
The basic principle is to maintain a normal connection state according to manufacturer specifications.
The battery is a component that stores electricity,
but the battery terminals are the initial entry point for sending that electricity to the car.
Precisely because it's a small contact point, its condition is crucial for considering the vehicle's electrical environment.