Get to know your car battery
Tom Vondrasek | 1st Dec 2023 | 6 minutes to read
Car batteries or start batteries, to call them by their function, have been around since the early 1900’s. To start a combustion engine back then, you needed to manually crank it over, so putting on an electric starter motor was a revolutionary change. Having a starter motor allowed drivers to turn a key or push a button instead of hand-cranking to start their car, which made the process much less of a chore.
Well over 100 years later, the principle and even technology is still the same. The battery is a plastic box with 2 terminals (+ & -) that contains an acid (electrolyte) and lead plates. This box generates electricity and is a standard lead acid battery (also known as a wet cell battery).
To start a petrol or diesel engine you still need a battery. Once it starts the alternator or generator kicks in and provides the electrical power. They even recharge the battery, so you are ready for your next start.
Below are some of the important elements of various different battery types and their applications:
Start Batteries Explained
Electronics
Start batteries have one primary role and that is to start the engine. In a modern vehicle, their secondary role is to keep the electronics alive before the engine is restarted. Even with the car turned off, there are certain items that remain powered up. The best examples are the central looking system and the clock on your dash. Both need power to run otherwise you would not be able to lock and unlock your car and you would need to reset the time, every single time you started the car.
The electronics draw very minimal power compared to starting the engine and will eventually flatten the battery. We are talking months and months of not being used for this to happen and this time frame is dependent on your battery’s condition.
Battery Power (CCA)
The power required to start an engine is immense. The battery normally only needs to supply it in short bursts if your engine is healthy. If you have ever tried to start a vehicle that had a starting problem with the engine, you can hear the battery lose its power the longer you try and start it. That is why short bursts are better than longer duration start attempts. It gives the battery a chance to recover between starting attempts.
This immense power is measured in CCA or Cold Cranking Amps. Broken down:
- Cold – The engine is cold or has not been started. This takes more power than a warm engine.
- Cranking – Rotating or turning over the engine
- Amps – The Ampere is an electrical measurement for current flow. The greater or higher the number of Amps, the more electricity flows down the cable.
Start batteries all have this rating (they are tested on it) and it represents the amount of current a battery can supply for 30 seconds at 0 degrees Fahrenheit.
Engine Size, Petrol & Diesel
Battery size gets larger with the size of your engine. A 2 litre, 4-cylinder engine needs a smaller battery than a 5 litre V8. Imagine putting a crank handle on both these engines and trying to turn them over or rotate them by hand. The V8 would require a lot more effort.
A diesel engine due to its makeup requires a larger battery than a petrol engine. For example, a 2-litre petrol engine will have a smaller battery than a 2-litre diesel engine. The reason why is that a diesel uses higher compression than a petrol engine. Higher compression creates more resistance to rotating or turning over the engine. It needs more power to overcome this and therefore needs a bigger battery.
Stop Start Vehicles
These vehicles are unusual as not only does the battery need to start the car, but it also needs to run the car while the engine is off. When the car comes to a stop, the engine turns off. When this happens the alternator that provides electric power stops working and the car needs to run off the battery. Once the accelerator is pressed the engine restarts and begins providing electrical power and recharges the battery. This technology was designed to save fuel, so you only used petrol when moving.
Due to the restarting after stopping during a trip and needing to power the vehicle when stationary these vehicles need a large battery. They also need a battery that can recharge faster than normal. This means the battery makeup is not a standard wet cell battery and will instead be an EFB (Enhanced Flooded Battery) or AGM (Absorbed Glass Mat) battery.
Hybrid Vehicles
Hybrid vehicles run 2 batteries.
- One is a large Stop Start type battery used to start the vehicle’s combustion engine. This is recharged through the engine’s alternator as in a normal engine driven vehicle.
- The other battery is like a mini-EV (Electric Vehicle) battery pack. You cannot plug it in and recharge it like a normal EV (Unless you have a plug-in Hybrid) and it is instead recharged through regenerative braking and the combustion engine’s alternator.
Selecting the Correct Start Battery for Your Vehicle
Selecting the correct start battery is not so difficult when your old one needs replacing. You can simply use our vehicle finder to get correct fitment. There are usually a number of options given for the following reasons:
Warranty – Start batteries can have different warranty periods so the longer it is, the higher the price of the battery.
CCA - Sometimes battery CCA can vary. Usually not by a lot. The higher the CCA, the greater the price of the battery.
Batteries are not cheap so having a choice allows you to suit your budget. When buying make sure the terminals are in the same spot as your old battery so the cabling will fit.
When it comes to replacing a start battery always check your owner’s manual. Most are extremely simple and straight forward and require basic hand tools to take out and replace the battery.
With later model computers you can use a small 9V battery to keep the computer going when changing over the start battery. You can get these at auto stores.
As mentioned earlier, the battery powers some items even when the vehicle is switched off. If you don’t keep power going when disconnecting the old battery and installing the new, these items may need to be reset (including the internal clock).
With some cars like stop start and hybrids, they monitor the battery, and it may need a scan tool to reset the monitor. In this instance, the 9V battery trick doesn’t work as you basically need to tell the car, “Hey, I changed your old battery for a new one.”
