What Wrench Do You Need to Change a Battery?

For most cars, a 10 mm wrench or socket is what you need to loosen and tighten the battery terminal clamps; many hold-down brackets use 10 mm or 13 mm, and GM-style side-post batteries typically use 8 mm (5/16 inch). That’s the quick answer. In practice, battery hardware varies by make and model, so having a small range of metric sizes (8–13 mm) and a ratchet with an extension covers nearly all 12-volt automotive batteries. Always remove the negative (black) terminal first and use insulated tools to avoid sparks.

The Most Common Wrench Sizes by Battery Hardware

Battery terminals and brackets aren’t standardized globally, but a handful of sizes dominate modern vehicles. Here’s what you’re most likely to encounter when replacing a 12-volt car battery.

• Terminal clamp pinch bolts (top-post batteries): 10 mm on most modern cars (some 8 mm, 12 mm are possible).
• Side-post terminal bolts (common on many GM vehicles): 8 mm or 5/16 inch hex.
• Hold-down clamp or crossbar bolts: commonly 10 mm or 13 mm; some older or larger vehicles may use 1/2 inch or 12 mm.
• Remote/jump posts under hood (battery located elsewhere): often 10 mm or 13 mm covers the protective covers or cable fasteners.

If you bring one tool, a 10 mm combination wrench or a 10 mm socket on a 1/4-inch-drive ratchet with a short extension will handle most terminal clamps, while adding 8 mm (or 5/16 inch) and 13 mm sockets covers side-posts and many hold-downs.

How to Choose the Right Wrench Quickly

If you’re standing at the parts store or your driveway and need to decide fast, these quick checks help you pick the correct wrench and stay safe.

• Check the terminal type: top-post clamps usually use a 10 mm pinch bolt; side-post batteries have a recessed bolt head that’s typically 8 mm (5/16 inch).
• Inspect the hold-down: J-bolts, clamps, or crossbars are often 10 mm or 13 mm. If you can’t see, plan for both sizes.
• Prefer sockets over adjustable wrenches: a 6-point socket reduces the chance of rounding small fasteners.
• Use an insulated or taped wrench if working near the positive terminal to reduce short-circuit risk.
• Confirm with the owner’s manual or a quick lookup of your vehicle year/make/model if available.

A compact metric socket set (8–13 mm) with a ratchet and 3–6 inch extension solves almost every battery removal without guesswork.

Tools and Materials Checklist

Before you begin, assemble the essential tools and protective gear to make the battery swap safer and faster.

• Wrenches/sockets: 10 mm (must-have); also 8 mm or 5/16 inch (side-post), 12 mm, and 13 mm for hold-downs.
• Ratchet with 3–6 inch extension (1/4-inch drive is ideal for tight spaces).
• Terminal cleaning brush or small wire brush for corrosion.
• Gloves and eye protection (acid and corrosion safety).
• Battery terminal protector or dielectric grease (optional, helps prevent corrosion).
• Torque wrench: inch-pound for terminals, foot-pound for hold-down (if you have one).

With these items on hand, you’ll be equipped to handle most battery changes neatly, safely, and without damaging hardware.

Quick Step-by-Step Procedure

Use this concise sequence to replace a typical 12-volt car battery without causing electrical issues or damaging components.

1. Turn off the vehicle and remove the key; open the hood and identify the battery or remote terminals.
2. Loosen the negative (black, “-”) terminal first using a 10 mm wrench/socket; lift it off and secure it away from the post.
3. Loosen the positive (red, “+”) terminal next using the appropriate wrench; remove and secure away from the post.
4. Remove the battery hold-down (often 10 mm or 13 mm); lift the battery straight up with both hands or a strap.
5. Clean the terminal clamps and tray; place the new battery, matching polarity orientation.
6. Reinstall the hold-down snugly; avoid overtightening.
7. Connect the positive terminal first, then the negative; tighten just enough to prevent movement.
8. Apply terminal protector if desired; confirm the battery is secure and cables don’t twist.

Following this order—negative off first, negative on last—reduces the risk of short circuits and protects sensitive electronics.

Safety and Torque Guidance

Battery replacement is straightforward but involves high current and corrosive material. These precautions help keep you and your vehicle safe.

• Always remove negative first and reconnect negative last to minimize short risk.
• Avoid contacting the wrench between the positive terminal and any metal ground.
• Wear eye protection; battery acid and corrosion can irritate skin and eyes.
• Typical terminal clamp torque: around 5–8 N·m (45–70 in-lb) for top-post; around 8–10 N·m (70–90 in-lb) for many side-post bolts. Hold-downs are often 13–20 N·m (10–15 ft-lb). Check your owner’s manual for exact specs.
• Do not overtighten small terminal bolts; it can crack the battery post or strip the fastener.

If you don’t have a torque wrench, tighten until secure and the clamp does not rotate by hand, then stop—excess force can cause costly damage.

When Not to DIY

There are situations where a professional technician—and specialized tools—are the safer choice.

• Hybrid and EV high-voltage batteries: never attempt; these require certified procedures and equipment.
• Vehicles needing computer support: some cars benefit from “memory saver” tools or specific relearn steps.
• Severe corrosion, swollen cases, or leaking batteries: handle with care and seek professional disposal/replacement.

When in doubt, a shop can install the battery, apply correct torque, and perform system checks quickly and safely.

Bottom Line

For changing a typical 12-volt car battery, carry a 10 mm wrench or socket for the terminal clamps and a 10 mm or 13 mm for the hold-down. GM-style side-post terminals usually need an 8 mm (5/16 inch) socket. Work negative-first, use insulated tools, and tighten just enough to secure—checking your vehicle’s manual when possible.

Summary

Most battery terminals use a 10 mm wrench or socket; hold-downs are commonly 10 mm or 13 mm; side-post bolts are typically 8 mm (5/16 inch). A small metric socket set (8–13 mm) plus a ratchet and extension will cover nearly all 12-volt battery swaps. Remove the negative cable first, reinstall it last, and avoid overtightening by following your vehicle’s torque specs.

What size nut goes on a car battery terminal?

The most common car battery terminal nut and bolt sizes are 10mm for the bolt head (using a 10mm wrench or socket) and 5/16-inch (or 3/8-inch for side terminals) for the bolt diameter, with 10mm often fitting the bolt head on a 5/16″ bolt. However, exact sizes can vary by vehicle, so it’s best to check your specific battery or take the old bolt to an auto parts store for an accurate match.
 
Common Sizes and Considerations:

• Wrench/Socket Size: A 10mm wrench or socket is the most frequently used size for the hexagonal nuts found on most top-mount battery terminals. 
• Bolt Diameter (Thread Size):
  • 5/16 inch: (approximately 7.9mm) is a very common diameter for the bolt that goes through the battery cable’s ring connector and into the terminal post. 
  • 3/8 inch: (approximately 9.5mm) is a common size for the bolts on side terminal batteries. 
• Variations: Some vehicles may use a 13mm wrench, though this is less common than 10mm. You may also encounter other, smaller metric bolt sizes on the terminal itself. 

How to Find Your Exact Size:

1. Check for the size on the existing nut: Opens in new tabLook for the size (e.g., “10mm,” “5/16”) on the bolt head or the nut itself. 
2. Take the bolt to an auto parts store: Opens in new tabThis is the most reliable method. Take the bolt with you to an auto parts store, and they can help you find the correct replacement nut and bolt. 
3. Use an adjustable wrench: Opens in new tabIf you don’t have the right size socket, an adjustable wrench can work, but be careful not to strip the nut. 

Safety Tip: Always disconnect the negative (-) battery terminal first to prevent accidental short circuits and potential electrical hazards.

What tools do I need to replace battery terminals?

To replace battery terminals, you will need a socket/wrench set to loosen the bolts, a wire brush for cleaning, and a battery terminal puller for removing stuck or corroded terminals. You should also wear safety glasses and gloves for protection against battery acid and sparks. Optional but helpful tools include a hacksaw, wire stripper, and battery terminal cleaner spray or baking soda mixture.
 
Essential Tools

• Socket/Wrench Set: Used to loosen the nuts on the battery terminal clamps. A combination wrench set is also useful. 
• Wire Brush: Essential for cleaning the battery posts and cable clamps to ensure a clean connection. 
• Battery Terminal Puller: A specialized tool that helps to gently remove terminals that are stuck due to corrosion, preventing damage to the cable. 
• Safety Glasses: Protect your eyes from potential battery acid or debris. 
• Work Gloves: Protect your hands from acid and ensure a firm grip. 

Optional Tools

• Hacksaw or Utility Knife: Can be used to cut away old, corroded sections of cable or to trim excess wires if replacing entire terminal assemblies. 
• Wire Stripper: If you are replacing the entire terminal, a wire stripper will be needed to remove the old insulation from the cable before attaching the new terminal. 
• Battery Terminal Cleaner Spray or Baking Soda Solution: A cleaner helps to neutralize corrosion on the battery post and cable. 
• Pliers: For general use in handling components and pulling cables. 
• Battery Memory Saver: Connects to the battery to maintain your vehicle’s electronic settings while the battery is disconnected, preventing loss of radio presets, clock settings, etc. 

This video shows how to replace battery terminals using various tools: 51sGreve’s GarageYouTube · May 13, 2023
Steps for Replacing Terminals

1. Disconnect the Battery: Opens in new tabAlways disconnect the negative (black) terminal first, then the positive (red) terminal. 
2. Clean the Cables: Opens in new tabUse a wire brush to clean the battery posts and the inside of the cable clamps. 
3. Remove Old Terminals: Opens in new tabIf the terminals are corroded and stuck, use a battery terminal puller to remove them without damaging the cables. 
4. Prepare New Terminals: Opens in new tabIf you’re installing new terminals, you may need to trim the cable and strip the wire to fit the new component. 
5. Attach New Terminals: Opens in new tabSecure the new terminals onto the posts and tighten them with the appropriate wrench or socket. 
6. Reconnect the Battery: Opens in new tabReconnect the positive terminal first, then the negative. 

What size wrench do you need to change a battery?

You will typically need a 10mm wrench to change a car battery, though an 8mm or 12mm wrench may also be required depending on the vehicle’s make and model. A standard open-end wrench or a socket wrench works, but a shorter wrench is recommended for the terminals to minimize the risk of shorting. Always disconnect the negative terminal first and reconnect it last to ensure safety. 
This video shows how to safely remove and install a car battery: 1mDad, how do I?YouTube · Aug 24, 2024
Why a 10mm Wrench is Common

• Standard Size: Many automotive battery terminals use nuts that are 10mm in size. 
• Versatility: It’s a common size for the nuts on the terminal clamps and potentially the battery hold-down bracket. 

Safety Precautions

• Order of Disconnection: Disconnect the negative (black) terminal first. 
• Order of Reconnection: Reconnect the positive (red) terminal first, followed by the negative terminal. 
• Use Insulated Tools: Use a wrench with an insulated handle to avoid accidental contact with the battery terminals or other metal components, which could cause a short circuit. 

Other Tools You May Need

• Socket Set: A socket wrench and extension may be needed to reach the battery’s hold-down bracket or if the battery has a cover. 
• Wire Brush/Terminal Cleaner: To clean any corrosion off the battery terminals and cables. 
• Anti-Corrosion Spray: To prevent future corrosion buildup on the terminals. 
• OBD-II Tool: For newer vehicles with advanced systems, you may need to register the new battery with the vehicle. 

What tool do I need to change my battery?

Tools You’ll Need
Safety gloves and goggles — we want you to learn how to change a car battery safely. Socket wrench — we recommend having several socket sizes available. Cleaning towels. Carbon wire brush or similar cleaning tool.