If you aren’t familiar with mechanical terminology this beginners guide to batteries will teach you the basics and the ‘not-so-basics’ of choosing your battery.
|Introduction to batteries|
A car battery is simply an energy storage device.
Your car uses the energy stored in the battery to operate the starter motor, ignition system, fuel injection system and other electrical devices for the engine during engine cranking and starting. It supplies all the electrical power for a car whenever the engine is not running and it helps the charging system provide electricity when current demands are above the output limit of the charging system.
The lead acid battery is made up of plates, lead, lead oxide and an electrolyte which is a solution made up of 35% sulphuric acid and 65% water. When the electrolyte interacts with the lead plates a chemical reaction occurs and produces electrons that create the voltage in a battery.
Another important part of the battery is the battery terminal or post. On each battery there are at least two posts. One will be a negative post and the other positive. The positive terminal will be marked with a ‘+’ symbol and/or with a red lead or cover. The positive post is sometimes larger than the negative post as well. The negative terminal will be marked with a ‘-‘ symbol and/or have a black lead.
CCA refers to Cold Cranking Amps.
This defines a battery’s ability to start an engine in cold temperatures. It measures the number of amps a battery delivers at -18 degrees C for 30 seconds without dropping below 1.2 volts per cell. The higher the CCA rating, the greater the starting power of the battery.
CA refers to Cranking Amps.
This rating used to describe the discharge load in amperes which a new fully charged battery at 0 degrees C can continuously deliver for 30 seconds and maintain a terminal voltage equal or greater than 1.2 volts. CA is also sometimes referred to as marine cranking Amps or MCA’s.
RC is Reserve Capacity.
It refers to the time in minutes a new fully charged battery will supply a constant load of 25 amps, without the battery falling below 10.5 volts. The higher the RC the longer your vehicle can operate if the alternator or fan belt fails.
AH refers to amp hours.
This rating is usually found on deep cycle batteries. If a battery is rated at 100 amp hours it should deliver 5 amps of power for 20 hours or 20 amps of power for 5 hours.
|Choosing a battery|
Before you start
The main things you need to consider when you choose a battery are size, power and warranty - it’s got to fit properly in your vehicle, deliver the right power, and be durable. The manufacturer’s specifications for your vehicle are a good place to start.
Basically there are two types of automotive batteries:
- The starting battery and,
- The deep cycle battery
The ‘starting battery’ is designed to deliver quick bursts of energy for starting engines and has a greater number of plates. Starting batteries shouldn’t be used for deep cycle applications as their life span will be drastically reduced.
The ‘deep cycle’ battery has less instant energy and more long term energy. The plates are thicker and can survive a number of discharge cycles. This type of battery is ideal for things like golf carts and operating 12 volt fridges and lighting.
There are various types of lead acid battery:
- The wet cell
- The Absorbed Glass Mat (AGM) and,
- The Gel cell
The ‘wet cell’ comes in two styles: serviceable and maintenance free. Serviceable means the water levels need to be checked and filled periodically whilst the maintenance free battery is generally sealed and requires little or no maintenance.
‘Absorbed glass mat’ and ‘gel cells’ are specialty type batteries. They typically cost more than a wet cell battery. They do store well and don’t tend to sulphate – that’s a condition that hardens the battery plates and reduces effectiveness - so they can be a good investment.