How do I prevent my car battery from going flat?

Something many of our keen eye customers will notice is the warranty sticker on top of the battery. This states that the battery needs to be kept above 12.1V and that if it reaches 10.6V then the warranty is voided. This article is crafted to elucidate the main causes of battery drain, helping you derive the most from your car battery purchased from reputable battery stores.

How does a car battery keep itself charged?

When you start your engine you use a small percentage of your battery capacity. While your engine is running the alternator is putting charge back into the battery and this will run the entire time the engine is on, meaning after 20-30 minutes of driving the battery will always be at full capacity. Depending on the type of battery you have, this alternator will put a certain charge voltage into the battery, 14.4V for a lead/acid and EFB and 14.7V for an AGM. When our customers come to us with warranty claims, one of the first things we ask is has the alternator been checked because if your alternator isn’t putting the appropriate charge voltage into the battery then the battery won’t be getting a complete charge.

Something that people may not be aware of is the fact that these batteries don’t like to be left at a partially discharged state. If you turn your car on and then immediately turn it off again this means that the battery hasn’t had enough time to be charged back to full by the alternator. If the battery is left in this state without being charged to full then it can cause sulfation to build up on the plates and this is what will ultimately kill the battery.

What is Sulfation?

Sulfation is one of the main causes we see for our customers batteries failing. It is also not covered under the warranty so it is very important to understand what it is and how to avoid it, in order to make sure you get the most out of your car battery.

All car batteries need to be kept above 50% capacity, 12.1V, as anything under this will cause sulfation to build up on the interior plates of the battery. Sulfation is not something you want as this will prevent the chemical reactions needed to accept and hold a charge. The biggest cause we see for sulfation is over discharge and this happens when the battery is in use while the engine is off, the alternator isn’t charging at the correct charge voltage or if the battery has been left connected to the vehicle for an extended period of time.

How do I prevent over discharge?

Over discharge is one of the biggest causes of dead batteries. It is important to understand how to avoid this as this isn’t covered under the manufacturers warranty and you may end up having to purchase a new battery years before it is necessary.

If your vehicle ever needs to be left for up to and over a week then parasitic drain can end up draining the battery below the 50% threshold. The most common cause of this would be the car alarm. We would always recommend that if the vehicle is being left for this amount of time then a battery charger should be hooked up to keep the battery trickle charged and above this 50% threshold. You can find our full range of Victron Smart Chargers here. We would recommend a smart charger as these will detect when the battery is fully charged and will prevent over charging.

How to find the right battery charger?

If you have ever tried to buy a battery charger you may find that there are a lot of options. The main rule of thumb is to keep the charge current between 10-20% of your overall battery capacity. You should be able to find your battery capacity on top of the battery. So for example, if you have a 90Ah battery then you would need a battery charger rated between 9-18A. Typically a 15A charger would suit most batteries, however we would recommend checking before purchasing.

Make sure your alternator is charging correctly.

One thing I have consistently mentioned throughout this article is the alternator, as your alternator is essential to making sure your battery is charged. If you believe you are having issues with your battery charge then it is important to first get the alternator checked to ensure that this is putting in the appropriate charge back into the battery. Additionally, it is important to check that the battery is the correct type for the vehicle as if it is the wrong chemical type then it won’t be getting the correct charge voltage, despite the alternator working fine. If you are unsure if the battery in your vehicle is correct then you can use our reg finder to check or you can get in touch with our customer support team who will be able to advise you.

Lastly, it is important to ensure that once the engine has been turned over you are leaving the alternator at least 20 minutes to put the charge used back into the battery.