Car Battery Basics: What You Need to Know Before Selling Your Car

Have you ever had it happen to you? You’ve finally cleaned your car, it’s looking great, pictures are ready to go – and then you try to start it. Click. Nothing. Flat battery.

Whether you're still using your car or it's sitting idle waiting to be sold, your battery needs attention. A flat or dodgy battery is one of the fastest ways to scare off a buyer – especially if they show up for a test drive and the thing won’t start.

Here’s what you need to know to keep your battery in good shape before you sell.

Why Car Batteries Fail

Car batteries aren’t built to last forever. Most last 3–5 years, but if you’ve been doing lots of short trips, leaving it parked up for long periods, or running dashcams and chargers, it can drain faster.

Key signs your battery might be struggling:
• Sluggish start when you turn the key
• Dim headlights when the engine’s off
• Dashboard battery light coming on
• Clicking sound when starting

How to Keep Your Battery Healthy

Start it up regularly
If you're not driving much, start the engine once a week and let it run for 15–20 minutes. That keeps the alternator charging the battery and stops it going flat.

Use a trickle charger
If your car is parked for weeks at a time, invest in a trickle charger (aka battery maintainer). It keeps the charge topped up without overcharging – perfect if you’re prepping a car for sale but not using it.

Turn everything off before you lock up
Headlights, interior lights, and infotainment screens can all drain power if left on – especially in older cars.

What to Avoid (Common Mistakes)

Don’t leave it flat for long
A dead battery that sits flat for days or weeks can become permanently damaged. Recharge it as soon as possible.

Don’t keep starting it and turning it off
Frequent short starts without driving don’t give the alternator time to recharge the battery. It’s better to let it run for at least 15 minutes.

Don’t disconnect the battery unnecessarily
Unless you're doing electrical work or storing the vehicle long-term, avoid removing the battery. It can mess with electronics and may reset key systems like your radio or immobiliser.

Don’t ignore corrosion
A build-up of white or blue powder around the terminals can block the flow of electricity. If you think it’s becoming an issue, let a professional handle it or, in many cases, it’s easier and cheaper to just get it replaced.

Don’t jump-start recklessly
Jump-starting with the wrong cables or in the wrong order can damage your vehicle’s electronics. If you’re unsure, get help or have it professionally charged.

Can You Check Battery Health Yourself?

Yes – and it's easier than you'd think. You can buy a cheap battery tester to check voltage. Follow the instructions carefully: attach the red clip to the positive terminal and the black clip to the negative terminal.

What the readings mean:
• Healthy battery: 12.6V+
• Below 12.4V: It’s weakening
• Below 12.0V: It’s on its last legs

Some garages or car parts shops will test it for free if you ask nicely.

Should You Replace It Before Selling?

It depends. If the car's struggling to start or the battery’s more than 4 years old, it’s probably worth replacing. A new battery gives buyers confidence and avoids that awkward “uhh… it won’t start” moment.

If you don’t want to replace it, just be honest in the listing. Mention that it’s fine with regular use but might need replacing soon.

Quick Tips Recap

• Start it weekly or use a trickle charger if it's parked up
• Turn off all electronics when not in use
• Check the age and voltage of your battery
• Don’t ignore slow starts or warning lights
• If it’s flat, charge it before showing it to buyers!

Final Tip: Keep it Simple

Keeping your battery healthy doesn’t need to be complicated or expensive. Focus on the basics and don’t get sucked in by clever marketing. A few good habits are all you need to keep your car starting strong.

Thinking of selling soon? Get your free online quote and we’ll handle the rest at Cash For Cars.

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