Expert advice: how to check for a flat battery

two red and two black jump leads placed on top of a car engine

With cold weather, or cold snaps, we see an increase in the number of call outs for cars with a flat battery.

The reason for this is simple: the older a battery gets, the less able it is to hold its charge in lower temperatures. And the colder the weather, the thicker oil gets, so the starter motor needs to draw more current from the battery to turn the engine over.

Put these together and tired car batteries are far more likely to fail. Here’s everything you need to know about your battery.

What to look out for

The weaker a battery gets, the more it struggles to supply the starter motor with sufficient current. So, listen out for what sounds like the engine turning over more slowly than normal.

Also, watch for a warning light in the dashboard (which looks like a red battery) coming on as you’re driving. This can be an early warning that the engine’s alternator isn’t charging your battery properly.

How to check your battery

If your vehicle is showing any of the above symptoms, take it to your nearest garage or fast fit centre. Ask them to perform a battery test and it will tell you what state your battery is in. Most places will do this for free.

What to do if you’ve got a flat battery

Calling your provider is a good start. Some may test your battery, jump start it, or get you to a garage.

Many Green Flag Technicians will be able to test your battery to see if it is faulty. Some may test other relevant vehicle systems for potential faults. If the battery is faulty, we may be able to replace the battery subject to availability.

What not to do if you’ve got a flat battery

Whatever you do, don’t ignore it.

Even if your breakdown cover provider gets you going again, don’t assume that’s the end. If your battery is old, you may need a new one to prevent getting a flat battery more regularly.

How to maintain your battery

Batteries always used to be under the bonnet, but increasingly we’re seeing them in the boot or even under the back seats. The handbook will say where your car’s is located.

Get started by checking the terminals aren’t covered with what looks like white fur. This is a by-product of the fumes that come off the battery. A wire brush will get rid of this and a bit of good old copper grease will stop them furring up.

Just be careful. Remember you’re playing with enough electricity to hurt!

Tabs and charging

Modern smart chargers make charging a modern battery super simple.

These chargers can be left connected to your vehicle battery without the risk of damaging the battery. They will also help extend the life of your battery.

How long should a battery last?

Most batteries now come with either three or five year warranties. And you’ll generally find they perform their best for around five years.

Battery technology has improved over the years with the introduction of EFB (Enhanced Flooded Batteries) and AGM (Absorbed Glass Mat) batteries. But with modern vehicle systems such as heated seats, there’s more strain put on the vehicle battery.

A flat battery can give your journey a decent delay, so check on it regularly.

The original article was written by Nick Reid, a fellow of the Institute of the Motor Industry and head of transformation at Green Flag. And has since been updated by John Price, one of Green Flag’s Automotive Technical Support Engineers.

2 comments on “Expert advice: how to check for a flat battery

  1. Abi Bradley 25/06/2015 8:31 AM

    Really helpful information, thank you!
    Car woudln’t start this morning and hoping Green Flag will be able to solve the problem when they come out this evening

  2. Carole 17/01/2017 3:37 PM

    Useful to know. Green Flag quickly and efficiently started my car with a flat battery today and advised me about trickle chargers. Very pleasant helpful man. Thank you.

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