Electric vehicles (EVs) are becoming increasingly popular, but questions about their maintenance and storage still linger, especially for those new to EV ownership. One common concern revolves around the 12V car battery – a component that, despite the high-voltage battery pack powering the vehicle, remains essential for auxiliary functions. When considering long-term storage, many car owners naturally think of using a Car Battery Trickle Charger to maintain the 12V battery’s health. But is this necessary or even recommended for EVs?
This article delves into the specifics of car battery trickle chargers in the context of electric vehicles, particularly addressing the scenario of storing your EV for extended periods. We’ll explore whether EVs utilize the high-voltage battery to maintain the 12V battery during storage, and what alternative approaches might be more suitable to ensure your EV is ready to go when you are.
Many might assume that an EV’s sophisticated system would automatically keep its 12V battery topped up, much like how a conventional car’s alternator recharges the battery while the engine is running. There’s a common misconception that the high-voltage battery pack in an EV will continuously “trickle” charge the 12V battery, even when the car is parked and seemingly off. However, this is not typically the case, especially when the vehicle is in storage.
In reality, the high-voltage battery in most EVs, including models like the BMW i3, primarily charges the 12V battery only when the car is in the “Ready” state – essentially, when it’s powered on and operational. When an EV is parked and turned off for storage, the high-voltage system is generally inactive in terms of charging the 12V battery.
Despite being inactive for driving, an EV still has various systems that draw power from the 12V battery even when parked. These can include:
- Remote receiver: For key fob functionalities and remote app access.
- Comfort Access electronics: Systems related to keyless entry and vehicle settings.
- Clock and memory functions: Maintaining time, date, and vehicle settings.
- Alarm systems: Ensuring vehicle security.
These systems, while minimal individually, contribute to a continuous drain on the 12V battery over time. This is why, even with a healthy battery, you might find a depleted 12V battery after storing your EV for several months without any intervention.
So, if the high-voltage battery isn’t trickle charging the 12V battery in storage, and there’s a consistent drain, what’s the best course of action? One approach, particularly favored by experienced EV owners, is to disconnect the 12V battery entirely during long-term storage.
This method directly addresses the battery drain issue by eliminating the parasitic load from the car’s systems. Modern Absorbent Glass Mat (AGM) 12V batteries, often found in EVs like the i3, are known for their low self-discharge rates compared to traditional flooded-cell batteries. This characteristic makes them well-suited for storage, often negating the need for a car battery trickle charger. Manufacturers of cars with AGM batteries sometimes even advise against trickle charging during storage, as these batteries are designed to hold their charge effectively when not in use.
For instance, an EV stored with its high-voltage battery around 40-50% charge and its 12V battery disconnected is likely to fare well over a 5-month storage period. The lithium-ion high-voltage battery itself has a very slow self-discharge rate, meaning it will retain a significant amount of its charge even after months of inactivity, especially as there are no high-voltage loads draining it in storage. Storing a lithium-ion battery at a moderate charge level, rather than at 100%, is also considered better for its long-term health.
Upon returning from storage, reconnecting the 12V battery and plugging in the EV to charge will replenish both the high-voltage and 12V batteries. While disconnecting the 12V battery for an extended period is generally safe, one potential side effect to be aware of is the possible loss of some stored vehicle information, such as trip data or charge level history, depending on the car model.
In conclusion, while the idea of using a car battery trickle charger for an EV in storage might seem intuitive due to conventional car practices, it’s often unnecessary and potentially not the optimal approach. Disconnecting the 12V battery, especially for EVs equipped with AGM batteries, is a viable strategy to prevent battery drain during long-term storage. This method, combined with storing the high-voltage battery at a moderate charge level, can help maintain the health of both batteries and ensure your electric vehicle is ready for your next drive.
