Your Guide to the Car Battery

Posted on November 29th, 2013 by GEM Motoring Assist

Car battery failure is one of the most common causes of an engine refusing to start and Rob Marshall advises that extra checks are necessary to reduce the chance of an annoying wintry inconvenience.

Car Batteries

It can be illogical for an otherwise reliable vehicle to fail to start at the first sign of a cold snap. The truth is that lower temperatures place its mechanical components under extra stress but a few simple checks will reduce the chance of your car battery letting you down.


Although requesting a garage to supply and fit a car battery for you is the most convenient option, many people prefer to buy the part from either an online or high-street retailer.

The first thing to check is whether or not the battery will fit physically into your car and you should measure the length, width and the height in millimetres. Most car batteries are identified by a three-digit code that highlights this, such as ‘063′ or ‘096′. Then, confirm that the position, size and shape of the terminals are the same as your replacement.

Car Batteries

The next step is to confirm whether or not your car battery is powerful enough. A Cold Cranking Amps (CCA) figure is given, indicating how capable the battery is at starting a cold engine. If your motoring consists mainly of short journeys, it may be advantageous to buy a battery with a higher CCA than that which was fitted originally. Additionally, the Ampere-hour (Ah) rating ascertains the number of amps that the battery can provide over a 20 hours period. For example, a 60Ah battery will deliver 3 Amps for twenty hours.

Although battery lifespan depends on how it is used, most types last for between three and five years. As batteries cost more than the labour involved to fit them, paying a little extra for an extended guarantee, some of which can be up to five years long, can be a prudent move, especially if you cover a low annual mileage.


A car battery will be less efficient at low temperatures. Engines are also harder to ‘turn over’ in winter and, with the driver making greater use of electricity-sapping accessories that decrease the chance of the battery’s energy from being replenished, once the engine is running, a weak item will soon give way under the stress. 

Even if you are not adept at DIY, many garages offer a free test, which will identify whether or not the car battery is able to cope with the rigours of winter use. Take advantage of such special offers, when advertised.

Some car batteries are not sealed, which means the caps can be take off and the level of electrolyte can be maintained, by adding distilled water, until the level is just above the internal plates.

Even if DIY is your forte, most modern car batteries are sealed, meaning very little can be done to them, apart from ensuring that the terminals are clean. Green-coloured corrosion, which can affect the electrical connections between the battery and the vehicle’s terminals, can be dissolved by boiling water. Coating the terminals with Petroleum Jelly (such as Vaseline) will help to discourage corrosion from building in the future.

Dirty, loose or corroded connections can cause an intermittent contact that might fool you into thinking that the battery is at fault

Check that the battery is fixed to the car securely; from 2012, it is included in the MoT Test


It is important not to overwork the battery. If your engine does not start first time, operate the starter in ten second bursts and then turn the ignition off for 30 seconds, before trying again.

Turn off any electrical accessories as soon as they are no longer required. Heated rear windscreens tend to work in conjunction with heated mirrors and consume a lot of electrical energy. Lights also consume a lot of power but never turn anything off, if it will prejudice road safety. If you only tend to cover short journeys, it is prudent to take your car for a longer run, of at least 20 miles, which will help recharge the battery to an acceptable level. Even a modern car will deliver more power to the battery above idling speeds but never be tempted to leave your car unattended, on a driveway, with the engine running. Apart from anything else, it is illegal.

 Car batteries are charged by the alternator. If the alternator fails, or its belt slips, or breaks, the battery will not be replenished

Unfortunately, car batteries can freeze and the rate at which they do so increases depending on how discharged they are. If a battery has a very low rate of charge, the electrolyte’s PH value increases closer to that of water and becomes more vulnerable to freezing. Like water, if the electrolyte freezes, it expands, buckling the internal lead plates and rendering the battery useless. The plastic battery case may also split, emptying it of dilute sulphuric acid.

If a battery is left discharged for a long period, a chemical reaction occurs internally that can cause permanent damage, a process known as sulphation. This might be caused if your car is out of use for a long time, which is not helped by some electrical accessories, such as a clock or alarm system that drain the battery while it is parked. In this case it would be better to disconnect and remove the battery from the car and charge it slowly, using any one of the many car battery chargers on the market, which will replenish the car battery slowly. However, be aware that batteries give off highly explosive gases, when being recharged, and necessary safety precautions should be taken.

On more recent models, even disconnecting the car battery can cause problems with the electrical system. Therefore, you should read the instruction manual, or consult a technician, to see if there is a procedure, which will allow the vehicle’s computers to ‘power down’. Disconnect the negative terminal first and replace it last.

Batteries have a finite life and, although there are retail products available to rejuvenate a tired item, at best, they only tend to delay the inevitable new purchase.

The dashboard warning light only advises when the battery is not receiving any charge. It does not indicate a flat battery