When should you replace your car’s battery?

21 Jul 2022

The battery is the first mover of your vehicle. It allows your engine to start cranking before the alternator kicks in, and allows all of your accessories to receive energy and function, such as your headlights, dash lights, and head unit. Given all that your battery does in a vehicle, it’s not surprising that these have to be replaced regularly.


How often should I replace my battery?


Most sources agree that batteries will begin to wear down by about the three year mark, however if your vehicle and battery are well maintained, this can be extended to five years or more. With that said, there are certain things that can cause your battery to decay faster, and there are certain indicators that you can look for to determine whether your battery has nearly expired.


What can cause your battery to decay faster?


                Sitting Idle


For starters, if you go long periods without using your battery, your battery will become damaged much faster than if it is being used regularly. There are multiple factors that contribute to this happening.

Firstly, batteries have an inherent constant discharge rate. This means that regardless of whether they are being used or not, the battery will continue to drain down to zero. Secondly, due to many modern cars being fitted with alarms, and accessories being a constant (though minor) draw on the battery, this further adds to the constant discharge rate of the battery.  

When a battery is discharged below its minimum safe charge, this can cause your battery to decay at a much higher rate than if the battery was being used.

The benefit to using the battery in your vehicle regularly is that your alternator will be able to charge the battery as you drive. This offsets the discharge inherent to the battery and in-vehicle accessories, meaning that your battery shouldn’t discharge below its maximum capacity.


                Excess Heat


Excessive heat will also decrease the lifespan of your battery significantly. As batteries are driven by chemical reaction, an increase in heat will cause this chemical reaction to increase in its rate of reaction. Though this will cause your battery to perform better in the short term, this can cause build-up on the metal plates within your battery, reducing performance over time as well as leeching out reactive elements within the electrolytes of the battery, thus causing a reduction in capacity.


What should I look for?


When determining whether your battery needs to be replaced, you should look for the following key indicators: start-up time in winter (or an inability to start in winter), time taken to tick over in other seasons, and your vehicle’s battery light being on.

When your vehicle takes time to start up at any time of the year, this generally means that the battery is completely discharged. Assuming that you haven’t left your headlights or interior lights on overnight, this will often be due to a reduction in battery capacity. As stated above, this can be due to excessive usage or past overheating. It is also worth noting that, although it isn’t a reasonable temperature for most parts of the world, a battery’s capacity is reduced by 50% at -22®c. While this may not be a reasonable figure to work from, even at 0®c on a particularly cold day in Australia, this can still be a significant reduction in battery capacity.

There are many things that we can do to help care for our car batteries, but hopefully you have some new tools that you can use to diagnose your battery issues or even extend the life of your batteries!