Batteries and electrical parts

Today's cars rely on electrics for almost everything: starting, charging, lighting, safety systems, engine management and comfort features. Electrical faults can be frustrating to diagnose, and electrical parts can be expensive and fussy about compatibility. This guide covers batteries, charging and starting parts, lights and sensors, and how to buy them without wasting money.

Diagnose before you buy

A car that won't start doesn't always need a new battery. Similar symptoms can come from:

• a battery at the end of its life;
• a faulty alternator that isn't charging the battery;
• a parasitic drain, where something keeps drawing power with the car off;
• a faulty starter motor or connection;
• corroded or loose battery terminals.

Many battery retailers and mechanics can test the battery and charging system. Testing first can save you buying a part you don't need. The WA Department of Transport's vehicle check fact sheet includes checking that the battery, wiring looms and connectors are all secure.

Choosing a car battery

When replacing a battery, match:

• physical size so it fits the tray and hold-down;
• terminal layout and type, so the cables reach and connect correctly;
• battery type, such as conventional flooded, enhanced flooded or AGM;
• ratings specified for your car, such as cold cranking amps and capacity.

Cars with stop-start systems often need a particular battery type designed for frequent restarts. Fitting the wrong type can shorten battery life or cause faults. Check your owner's manual or ask the retailer to look up your car.

Some modern cars need the new battery registered with the car's computer or settings reset after replacement. Check before you start, or ask a professional to do it.

Handling batteries safely

• Wear gloves and eye protection.
• Follow the manual's order for disconnecting and reconnecting terminals.
• Don't let tools bridge the terminals.
• Keep sparks and flames away.
• Secure the new battery with its hold-down.

Alternators and starter motors

Alternators and starter motors are commonly available new, remanufactured or used. When buying:

• match the part number or confirm fitment using your VIN;
• compare mounting points, pulley type and electrical connectors;
• ask whether a core deposit applies, and return the old unit to get it back;
• compare warranties between new, remanufactured and used.

Our quote comparer lets you include freight, fitting, refundable cores and warranty months in one comparison.

Lights and bulbs

Lights help you see and be seen. When replacing bulbs or light assemblies:

• check the bulb type in your manual or on the old bulb;
• replace headlight bulbs in pairs so brightness and colour match;
• avoid touching halogen bulb glass with bare fingers;
• check that replacement lights suit your vehicle and meet the rules in your state.

The WA Department of Transport's checklist includes checking high and low beam headlights for operation and alignment, and checking all lights for cracked, faded or damaged lenses.

Sensors and modules

Sensors, control modules and electronic parts can be the most difficult to match. Small differences in part numbers, plugs or software can stop a part working, and some modules need programming to your car. Before buying:

• use the part number from the old part;
• confirm compatibility with your VIN;
• ask whether programming or coding is needed;
• check the seller's return policy for electrical parts.

Used modules may be coded to their original vehicle and might not work in yours without reprogramming.

Buying used electrical parts

Used electrical parts from recyclers can save money, but check:

• the part number and connectors match;
• there's no damage, corrosion or water entry;
• whether the part has been tested;
• the warranty and return terms.

Our guide to used parts and wreckers has more.

Your rights

When you buy from a business, consumer guarantees apply. Consumer Protection WA explains that sellers must provide a remedy if products aren't of acceptable quality, aren't fit for a specified purpose or don't match their description. A seller's restrictive returns policy on electrical parts can't remove those rights, although whether a part was fitted correctly may matter in a dispute. Keep receipts and records of who fitted the part.

Recycling old batteries

Recycling Near You says lead-acid car batteries contain lead, lead compounds and sulfuric acid and are classified as hazardous waste. Don't put them in household rubbish. Almost all scrap metal merchants accept them, and collection services are available at most landfills, transfer stations and automotive workshops. See our recycling guide.

Hybrid and electric vehicles

Hybrid and electric vehicles have high-voltage battery systems that can be lethal. Leave any work on high-voltage components to qualified technicians.

Signs of a failing battery

Common warning signs include slow cranking when starting, dim lights at start-up, a battery warning light, corrosion around the terminals and needing frequent jump starts. Batteries often fail with little warning, especially in extreme temperatures. If your battery is getting old or showing these signs, have it tested before it leaves you stranded.

Jump-starting safely

If you need a jump start, follow the procedure in your owner's manual, because some cars specify particular connection points. Connect the leads in the correct order, keep the leads away from moving parts and don't let the clamps touch each other. If a battery is cracked, leaking or frozen, don't try to jump-start it.

Looking after your battery

• Keep terminals clean and tight.
• Make sure the battery is held securely.
• If the car isn't used for long periods, consider a suitable battery maintainer.
• Avoid leaving lights or accessories on with the engine off.
• Have the charging system checked if batteries keep going flat.

Wiring and fuses

Many electrical faults come down to simple causes, such as a blown fuse, a corroded earth connection or a damaged wire. Check the fuses listed in your owner's manual before buying expensive parts. Always replace a fuse with one of the same rating. If a fuse keeps blowing, there's an underlying fault, and a mechanic or auto electrician should find it.

Auto electricians

Some electrical problems need a specialist. Auto electricians diagnose and repair electrical systems, from wiring faults to charging problems and accessories. For intermittent or complex electrical faults, an auto electrician can save time and money compared with replacing parts on guesswork.

Accessories and add-ons

Dash cameras, extra lights, fridges, sound systems and other accessories all draw power. Poorly installed accessories are a common cause of flat batteries and electrical faults. Have accessories installed by a qualified installer or auto electrician, use appropriately rated wiring and fuses, and check that the battery and charging system can handle the extra load. Some accessories, such as additional driving lights, also need to meet rules in your state or territory.

Key points

• Test the battery and charging system before buying parts.
• Match battery size, terminals, type and ratings, especially for stop-start cars.
• Match alternators, starters and modules by part number and VIN, and ask about programming.
• Compare new, remanufactured and used options, including cores and warranties.
• Recycle old batteries and leave high-voltage work to professionals.