How To Check Your Car Battery Life


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Your car’s battery life is one of those factors that you never think about until you go to start your car one day, and it just won’t crank. Modern cars are technological marvels that require constant battery power even when switched off to maintain the status of their highly sophisticated computer systems. With hybrids and EVs, battery life becomes even more crucial. In this article, we will explain everything you need to know about car batteries, as well as provide a top tip on how to keep everything in your car running smoothly by way of regular diagnostics, which anyone can do.

First, we will tell you about the purpose of the car battery, the kinds of batteries you may encounter, why you should periodically check their health status, how to check it, and also explain how solutions such as Carly can help you keep not just your car’s battery, but your entire car in good health.


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Why does my car need a battery?

In the early days of motoring, cars didn’t have batteries. If you wanted to drive them, you had to crank the engine by hand until it turned over. This proved to be quite tiring and could be dangerous if not done in the correct manner (broken thumbs due to improper gripping of the crank handle were most common). Therefore, the starter motor was soon introduced whereby pressing a button, or later on, turning a key would start the engine.

Of course, to enable a starter motor to start the engine, it would require a supply of electricity. Enter the car battery. The battery would be charged by the dynamo or generator (later on, alternator), and provide the necessary electrical power to crank the engine.

Fast forward to the modern era, and cars have a myriad of computer control systems that are connected to hundreds of sensors and miles of wire. The car battery now has to provide continuous power to these systems. Starting the engine is just one of its many responsibilities.

In case you’re interested, the main battery produces 12v DC and can provide upwards of 100 amperes in higher-capacity batteries used for larger displacement engines because in order to spin a large displacement engine with many cylinders at a speed fast enough for internal combustion to take over, a large current is required, albeit for a few seconds.

Car Battery
Car mechanic is checking the engine and holding the battery gauge.

What kinds of batteries are there?

Let us consider a regular, non-hybrid car. There’s one battery, which is referred to as “the battery”. This is the aforementioned 12v unit and can have current ratings as low as 45 amperes for hatches and smaller sedans, up to 100 amperes or more for full-sized luxury cars and SUVs. Some cars may even have two batteries. This battery is typically of the sealed, zero-maintenance type and can be a lead-acid battery, gel mat battery, absorbent glass battery, enhanced flooded battery, or similar. You don’t need to know the technical details of these, just remember to replace your car battery with one that has the same specifications when replacement time comes around.

Now, let us look at hybrids. A hybrid will have the battery as spoken above, often referred to as the “starter battery”, “12v battery” or “auxiliary battery”. In addition, it will have a second battery called the “main battery” or “hybrid system battery”. This battery is a high-capacity one that’s typically a lithium-ion or nickel metal hydride type, and produces in the order of hundreds of volts.

An EV or Plug-In Hybrid Vehicle (PHEV) will have the same type of battery as a hybrid battery, and may or may not have a 12v battery.

Where can I find the battery What kinds of batteries are there?

If you want to find the battery, let us be clear that it’s the 12v battery that you want to find. Don’t go messing around with the hybrid system battery, as the voltages and currents that it packs can easily kill you. In fact, even the 12v battery has enough current to start a fire, so be careful. Common places for the 12v battery are under the hood in the engine bay, in the trunk beneath a marked panel, underneath the front passenger seat or underneath the rear seat. Your vehicle’s owner’s manual will clearly state the location of the 12v battery.

For interest’s sake, hybrid and EV/PHEV batteries can be found beneath the floor of the vehicle, beneath the rear seat or in the boot. Manufacturers have developed creative ways to lay this battery out within the car’s frame, ensuring adequate passenger and cargo space, as well as handling dynamics.

Why should I check battery health?

Over time, your battery will degrade, and be able to hold less charge. This also means that it can provide less current for the starting of the engine, resulting in hesitant starts, long cranking sessions, and other electrical problems. Therefore, you should periodically check your battery’s health, especially if you have purchased a used car and aren’t sure of the age of the battery, or if it’s been more than two years since you installed a new battery.

How can I check battery health?

The easiest way is to grab a multimeter and check the voltage across the battery terminals. It should be greater than 12 volts with the car switched off, and no load. Upon starting the car, with the engine running, the voltage should rise above 13 volts, signifying a healthy charging system. However, unless you’re competent with electrical and electronic work, it’s best to not attempt this.

Some newer vehicles with sophisticated infotainment systems can actually allow you to view the battery health status via the system menu, so this is another avenue. However, if your vehicle is older and/or doesn’t have this functionality, a visit to a workshop where a diagnostic scan can be carried out is your best bet. Of course, this will cost you between $30 and $80, plus the cost of traveling, as well as time cost.

Can I do diagnostic scans by myself?

Yes, you can. There are a variety of consumer-grade solutions available to purchase that can cost as little as $25, and go well over $1,000. We would like to present a powerful, versatile, and cost-effective solution called Carly. Carly costs less than $100 for the hardware and software.

Carly is a two-part solution that’s been developed to work together. The hardware part is the Carly Universal OBD Scanner that plugs into your vehicle’s OBD2 port. If your vehicle’s year of manufacture is 2005 or later, it’s bound to have an OBD2 port, and the owner’s manual will reveal the location.

The software part of Carly is an app that can live on your Android or iOS smartphone. It can be downloaded via the respective app stores. Furthermore, the free Carly lite app allows you to check what’s available from Carly for your car before spending your money on the full solution.

What can Carly do?

Carly can do a whole lot of things. It can run complex diagnostic scans on your car, telling you the health status of each and every connected system. It can allow you to customize certain aspects of your car via the coding function. Carly also allows you to perform maintenance counter resets and re-initializations, such as after installing a new battery or doing an oil change. Finally, if you’re checking out a used car, the Carly Used Car Check will help you detect if it’s been a victim of mileage tampering. Carly truly is a wonderful solution that every vehicle owner and driver should use.

Keep in mind, that every car has different software and modules built-in. Therefore specific features will vary with every model.

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