Factors that Affect 12V Battery Life in EVs

by | May 31, 2024 | EV Battery | 0 comments

As EVs increase in popularity, two of the most prevalent objections to adoption are answered and quelled. Owners no longer worry as much – or at all – about range as they become more comfortable with charging options and their driving patterns, and the concern about finding locations to charge becomes far less of an issue. But one objection that still has yet to be answered in many minds is about EV battery life.

The typical EV battery is expected to last around 15 to 20 years, or between 100,000 and 200,000 miles for the average driver, but how long the 12-volt battery will last isn’t as clear. Since most EVs use top-tier options including Li-Ion 12V batteries, it should be far longer than the typical three-to-five-year span of a car battery.

What factors into how long an EV’s 12-volt battery will last? Here are some of the factors that affect EV battery lifespans, and what can be done to mitigate the degradation.

Heat and AC Usage

It’s well established that an EV’s range is significantly reduced in cold weather and winter conditions. While some of that range loss is because the battery’s own protective measures ensure the cells don’t freeze and get damaged, that’s certainly not the only consideration. When the weather is cold or freezing, the heat pump is used, consuming between 1kW and 5kW.

But there’s a distinction to be made. Although the heat pump is going, it’s almost always being powered by the traction battery. The HVAC fan, however, is powered by the 12-volt system. It’s a much smaller draw on the battery, but it does pull it from the 12-volt side. And whether you’re using the air conditioning or the heater, when the fan is on, it’s drawing down the 12-volt battery. Keep in mind that it’s there to be used and make you comfortable, and we’ll discuss the long-term effects later.

Advanced Drive Assistance Systems

Your typical passenger car’s average number of ADAS systems is increasing, but it seems that EVs contain virtually all of the available options from their respective manufacturers. And while they’re great to have for safety’s sake, each of the sensors and modules requires a current to operate, and they’re supported by the 12-volt battery.

Each camera, lidar, ultrasonic sensor, and radar requires power consumption, as do braking actuators, steering actuators, and so on. The 12-volt battery is in place primarily for safety power capacity, powering these functions.

Again, each of these sensors and modules requires a very small amount of energy to operate, but cumulatively, they can begin to affect the amount of power drawn by the 12V system.

Type of Battery

Like any other vehicle, the battery chemistry is a major determiner of how long the battery will last. For some carmakers, the battery they use for the 12V system is boasted to be a lifetime battery, and it may never need to be replaced under normal circumstances. That tends to be the case for Li-Ion batteries, but even then, there are reports that the battery fails in as little as one year – albeit, that’s an outlier and likely a defect. But for most EVs, the 12V battery is likely going to last around 10 to 12 years if it’s Li-Ion.

However, many carmakers still use lead-acid batteries for EV 12V batteries. These might be SLA in rare instances, and more likely in hybrids, and AGM batteries are relatively common. When an EV is used in normal circumstances, the battery could easily last six to eight years for an AGM, and even SLA batteries can extend past the normal three-to-five-year lifespan and creep up closer to six years.

Driving with Low Traction Battery Charge

One of the most prevalent killers for 12V batteries in EVs is when a traction battery is regularly driven with a low charge. Some carmakers have built in a ‘safeguard’ that prevents energy from being drawn from the traction battery for 12-volt accessories like heated seats when the charge is below 20 or 30%, and the step-down converter is also turned off or regulated.

Now, EVs use deep cycle batteries that are capable of handling deep discharges better than a standard lead-acid battery, but even they will deteriorate faster when exposed to deep discharges. It’s best to operate EVs above 20% charge to avoid some of the troublesome side effects your customers might not expect.

How Much Does It Matter Over the Long Haul?

As it relates to using the HVAC systems, both heating and cooling, the effects on the 12-volt battery are negligible. By far, the benefit of driving your vehicle comfortably will outweigh the nearly immeasurable amount of 12V battery lifespan you’ll give up.

The same is true for ADAS systems that your vehicle contains. Not only would you not want to give up the peace of mind and convenience that those systems bring to the table, but the minimal draw won’t truly affect battery life to any great degree.

Where it gets more interesting is when battery chemistry is introduced. It’s no huge revelation that Li-Ion batteries are the top of the line when it comes to deep cycle applications, capable of 5,000 deep discharge and recharge cycles or more in many cases. This alone will achieve years longer life in EV applications, even over AGM batteries. Will it affect your decision about which EV to purchase? Likely not, but it may factor into which replacement battery is chosen after the original fails.

The most important factor is ensuring the battery charges properly, and that’s something to do with driving habits. Ensure EV owners know that the traction battery charge affects how the 12-volt battery recharges. Maintaining a charge above 30% is ideal in all instances.

However, the most peace of mind comes from knowing that the battery’s condition is good on a regular basis. Whenever EV customers arrive in the service drive, treat them to the same battery test as your ICE customers receive. Equipment like the MVT handheld tester can produce fast results for all types of battery chemistries, and your customers can better grasp how their battery is doing as it ages.