Are you confused about what type of battery is best for your car? You’re not alone. There’s a lot of misinformation out there.
In this article I’ll explain the basic principles around how the electrical system in your car works, what types of accessories have what kind of power demand, what the most common types of car battery are, and how to select the right type to suit your specific needs.
THE ELECTRICAL SYSTEM
Before we dive in to the different types of batteries available, it’s important to understand a little bit about how the electrical system in your car works.
On a modern car, the battery has six basic tasks:
- Powering the alarm, and other fundamental electronics while the engine is off.
- Powering any aftermarket accessories which remain powered up while the engine is off (dash cam, etc).
- Powering the car’s electrical systems any time the ignition is turned on while the engine is off.
- Powering the starter motor to crank the engine.
- Filtering the power generated by the alternator when the engine is running.
- Providing reserve power should the alternator fail.
Once the engine is started, the alternator generates the power required to keep the car’s systems running and maintain charge in the battery. This is why you can jump start or roll start a car with a flat battery, or in some cases even disconnect the battery entirely on a running car (not advised).
At a fundamental level, the battery’s responsibilities can be broken down in to two basic categories:
- Provide stable voltage with relatively low amounts of current over long periods of time (when the engine is off).
- Provide short bursts of high current with minimal voltage droop (starting the engine).
The Alternator and Engine Control Unit (ECU) regulate the charge that the battery receives while the engine is running to prolong the battery’s life. This will be important to consider later on when we are discussing the different types of batteries available.
Now that you have a basic understanding of how the electrical system in your car works, lets take a look at some of the common types of aftermarket accessories, and their power requirements.
Dashcams: My guess is a lot of you are reading this because a dashcam that’s running 24/7 has killed your battery. It probably took a week or so the first time, then less and less on subsequent ocasions. However this does not mean that dashcams draw a lot of power. What dashcams do is draw a small amount of power, but over long periods of time. If you don’t drive your car much, the battery never gets the chance to charge back up, and ultimately your battery goes flat. Regardless of the battery fitted, if the battery never gets the chance to charge back up, it will always go flat. A higher capacity battery will just prolong the process, so proper power management is important. Make sure your dashcam installation has a safeguard that automatically switches off the dashcam when the battery voltage drops below around 12Volts. If you find your dashcam is turning off all the time, it’s time for a battery upgrade. many modern cars have safeguards to prevent damage to the electronics which stop the car from even attempting to start if the battery voltage is below 10.5Volts or thereabouts, so it’s important you don’t allow your dashcam to run the battery down that low.
Audio Systems: These vary a lot in their demands. Your typical head unit and speaker upgrade wont place enough additional load on the car’s electrical system to worry about, however if you’ve added high powered amps or subwoofers, then you may need to look at some upgrades. Lower frequency sounds require more energy to produce the same perceived volume, so a loud, bassy system can add a lot of transient strain to your electrical system. Every time the bass hits, a larger amount of current is drawn from the electrical system. It’s nothing like the power required to start the car, but a lot more than any other accessory in the average car. These transient spikes in demand are often more than the car’s alternator is able to supply, so the battery ends up doing some work (remember earlier when I said the battery acts like a power filter while the engine is running?). Actually it works more like a capacitor. You can learn more about that in my article about capacitors. Basically, if you have a loud bassy audio system, you’ll need a battery that can handle short, sharp and frequent power demands. If you have a really massive system, an upgraded alternator may also be required. The easiest way to tell is to look at your battery voltage while the car is running. if the voltage droops every time the bass hits, upgrades are needed. Additionally, if you like to use your system when the engine isn’t running, you’ll also need a battery that can handle sustained load for long periods of time.
Lighting: With the increased popularity of LED (light emitting diode) lighting, this is becoming less of a problem. LEDs are far more efficient than conventional filament style globes. Meaning they output more light and less heat, so there is a lot less power demand. If you’ve added some extra interior lighting such as coloured CCFL, Neon or LED, you wont need to worry about it as the increase in load is minimal. Likewise with things like underbody neons. However if you’ve added huge halogen spotlights to your car, it’s worth doing some basic tests to see if upgrades are required. With the car running, measure your battery voltage. It should read around 13.8 – 14.2Volts. Now switch on your aftermarket lighting. You may find the voltage drops momentarily while they start up. This isn’t a problem as long as the voltage drop is within around 0.5Volts. If its any more than that, or if the voltage doesn’t come back up to normal once the lights are running, upgrades are probably needed. you’ll need to look at a battery which can manage higher current draw for sustained long periods of time (similar to with a big audio system). However as the load is constant when the lights are on, you don’t need to worry about a battery which manages transient spikes. If the power draw from the lighting exceeds the alternator’s ability to charge the battery it will ultimately go flat, so an alternator upgrade may also be required, however this is unlikely.
Winches, Fridges, Pumps, etc: These can often require large amounts of power, and unlike lighting and audio accessories, are often used when the engine is off. Most serious off-road vehicles which use these have a dual battery system installed. One battery is used to power accessories, while the other is used to run the car’s systems. Charging is typically managed by some kind of control module, and an alternator upgrade is sometimes also required. You don’t want to end up stranded in the middle of nowhere, so it’s best to speak to a dedicated 4×4 specialist regarding the specific requirements of the system.
The important thing to remember in all this is that regardless of the battery fitted. If the power draw exceeds the alternator’s ability to charge it, the battery will ultimately go flat. A larger capacity battery simply takes longer to go flat. There’s no such thing as free power.
By now you should have a pretty good understanding of how the electrical system in your car works, and the demands of whatever aftermarket systems you’ve fitted, so lets move on to the most common types of battery available, and make some informed decisions…
Deep Cycle Battery: These are a popular choice among car audio enthusiasts, however they are typically not used for street cars because they have a high discharge rate, meaning the battery will run down very quickly under load. They are not a good choice for people wanting to run accessories like dashcams for long periods of time where the car is not being used, or people who need to run a lot of high power demand accessories such as spotlights or long periods of time.
Deep Cycle Batteries are popular among car audio circles as they can be reliably run down at a competition, then recharged without issue. For these reasons, they can be a great choice for vehicles such as boats and racecars which only require a battery to start, and are not used for long periods of time in between. They also perform well in extreme weather conditions. particularly cold.
Wet/Flooded Battery: These are one of the most popular types of batteries, primarily due to their low cost. These are sealed and maintenance free, unlike those old school batteries that needed to be topped up with distilled water. Wet/Flooded Batteries adequately handle the high current demands of starting an engine regularly, however they are not great at powering accessories for long periods of time while the engine is off. Most people will find this type of battery sufficient for their day to day needs, so long as they aren’t running a large audio system, or wanting the battery to last a number of days whilst running accessories with the engine off.
Calcium Battery: Calcium batteries are great at providing sustained voltage under moderate load for long periods of time. Which makes them a good choice for people needing to run accessories like dashcams or stereos for longer periods of time while the engine is off. The main disadvantage is that these batteries are easily damaged by overcharging, so tend to have a shorter lifespan than other types of battery.
VRLA battery: VRLA stands for a valve regulated lead acid battery. There two types of VRLA battery: Gel or AGM. A Gel battery uses silicon to make the acid more solid and like a gel. This type of battery performs very well in harsh cold environments and is great at supplying sustained current for long periods of time, but is not the best for a starter battery as they are not able to supply large amounts of current quickly.
The AGM battery uses absorbent glass matt. AGM batteries have a very low internal resistance, which make them perfect for starting a car, and handling transient spikes in current like you would find with a big audio system. They also handle sustained current for long periods of time, as well as deep cycling quite well too, which really makes them a great all rounder for just about any application. However they do tend to be more expensive than other common battery types. There are also other variations to this battery type, such as the ever popular Spiralcell technology used by Optima, which further increases performance.
Lithium Ion Battery: Used in some high performance cars. These batteries are lightweight and great at handling high demand engine starting, transient loads, as well as sustained power draw. They are also not bothered by charging and discharging which make them ideal for just about any conceivable application. However they are very expensive.
The final piece of the puzzle is capacity, and this is where a lot of people are most confused. Perhaps the most common misconception is that a battery with a higher CCA (Cold Cranking Amps) number will last longer, and be better at powering accessories for long periods of time, etc. This is simply not the case.
In this final section we’ll look at the different ways which a battery’s performance is measured and what each of them mean in real world terms…
Cold Cranking Amps (CCA): This simply measures the current (Amps) that the battery is able to supply in a 30 second at 0 °F (−18 °C), whilst maintaining at least 1.2 volts per cell (7.2 volts for a 12-volt battery). This is an important consideration in colder climates, and the CCA will in all cases need to exceed that of the factory fitted battery. The higher the CCA, the more easily the battery will be able to start the car.
Hot Cranking Amps (HCA): This is the same as CCS, but measured at 26.7 °C (80 °F ).
Cranking Amps (CA): Just like CCA and HCA, but measured at 0 °C (32 °F)
Ampere Hours (Ah): This one is a bit more confusing. Ampere Hours are a measurement of the battery’s capacity to maintain the flow of current at a rate of one Amp per hour. Basically the higher the number, the longer it will take for the battery to go flat. Remember that a high Ah rating doesn’t necessarily mean a high CCA or CA rating, so make sure these still meet or exceed that of the factory fitted battery. Generally, this measurement varies widely with the duration of the discharge period, therefore the value is typically only meaningful when the duration is specified. This rating is rarely stated for automotive batteries, except in Europe where it is required by law.
Reserve capacity minutes (RCM): Also referred to as reserve capacity (RC) is similar to “Ah” in that it measures a battery’s ability to sustain a minimum stated electrical load over time. More specially it measures how long a battery at 27 °C (80 °F) will continuously deliver 25 amperes before its voltage drops below 10.5 volts. This is the most important measurement when considering a battery that will be able to run your accessories for the longest amount of time while the engine is off, whilst maintaining enough charge to start the car. Again, the higher the number, the longer the battery will last when powering accessories with the engine off, but this does not account for cranking amps.
So how do I choose the right battery for my car?
Ultimately, the best battery for your car will depend on the size of the engine (bigger engines require more cranking amps to start), and the load placed on the battery while the car is running, and while it’s off.
An auto-electrician can perform what’s known as a parasitic load test, which measures how much current is demanded of your battery while the car is off, or while the car is running. This is the best way to figure out the most appropriately sized battery in terms of capacity, and if an alternator upgrade is required.
If you know the load in Amps when the car is off, as well as the rating of the battery in Ah, you can calculate roughly how long it will take for your battery to go flat using this simple equation:
Load in Amps ÷ (Battery’s Ah rating × 0.7*) = Expected battery life in hours
*The 0.7 in the equation allows for external factors which can effect battery life.
So you can see for example, if you have a 200Ah battery, and you know your car draws 0.5A when parked in the garage, it’s reasonable to expect the battery will last around 280 hours before going flat.
Don’t forget to also consider the physical size of the battery too as the capacity you want may not fit in your car.
Battery Council International group size (BCI): specifies a battery’s physical dimensions. So make sure you check compatibility with your car before purchasing.
The best battery for your car will be one that performs to your required characteristics as we discussed in the Battery Type section, has enough cranking amps to start your motor (matches or exceeds that of the factory fitted battery), and a RC or Ah rating high enough to maintain power to your accessories for the desired duration.