Short answer: Some 2015 Malibu configurations use a second 12-volt battery in the trunk to support the car’s electrical systems or mild-hybrid features, while most non-hybrid models keep the primary battery in the engine bay. If your car isn’t a hybrid, the trunk battery may be aftermarket or related to a specific trim.
In more detail, the presence of a battery in the trunk isn’t standard across all 2015 Malibu models. It’s more common on Malibu Eco/eAssist variants that use a mild-hybrid system to improve efficiency, where an auxiliary battery is used to power accessories and assist the hybrid components. In other cases, a trunk battery can also result from dealer options, regional specifications, or aftermarket installations. To know for sure, you’ll want to check your exact trim, VIN, and the owner’s manual.
Why GM would put a battery in the trunk
Before listing the typical reasons, it helps to understand the logic behind trunk-mounted batteries. The extra battery can free up space in the engine bay, help with vehicle packaging and weight distribution, and ensure ample electrical capacity for systems that run when the engine is off or when the vehicle uses start-stop or hybrid features.
In many configurations, a trunk battery supports start-stop operation by providing a reliable power reserve for engine-off periods and rapid reconnection when the engine restarts.
For mild-hybrid or eAssist setups, the trunk battery powers the hybrid/electric components and certain electronics, reducing the load on the main cranking battery.
Locating the auxiliary battery in the trunk can also protect it from engine bay heat and vibrations, potentially extending its life in some maintenance scenarios.
These arrangements are not universal. If you have a standard gasoline Malibu without hybrid features, a trunk battery is less common and may indicate a dealership option, a previous owner’s modification, or a configuration specific to certain markets.
How to tell if your 2015 Malibu has a trunk battery
Use these steps to confirm the setup on your exact car:
Open the trunk and look for a second battery or a battery box in the spare-tire area. A second battery is a clear sign of an auxiliary system.
Check the battery labels or markings. An auxiliary or “12V auxiliary,” “eAssist,” or similar designation often indicates a secondary battery separate from the main engine-bay battery.
Consult the owner’s manual or window sticker for trim-specific information about the electrical system and battery locations.
Inspect the engine bay: if there’s only one 12V battery in the engine compartment and a second in the trunk, you’re dealing with a two-battery setup.
If you’re unsure, a quick call to a Chevrolet dealer or a certified technician with your VIN can confirm whether your specific car has a trunk-mounted auxiliary battery and why it’s there.
What to do if you find a trunk battery
Follow these practical steps to maintain safety and reliability:
Do not disconnect or service the batteries while the vehicle is in a closed space or if you’re unsure of the procedure. If you need to inspect, consult a professional first.
Keep the battery terminals clean and free of corrosion; check for any signs of swelling or damaged cables.
If you’re replacing batteries, use the correct type and rating specified for both the primary and auxiliary batteries, and be aware that some systems may require reprogramming or reinitialization after replacement.
If you have electrical accessories added aftermarket (sound systems, lighting, etc.), ensure they’re properly wired and fused to avoid overloading the factory electrical system.
Impact on maintenance and service
When service involves electrical systems or battery replacement, technicians will verify both batteries and their charging circuits. In some scenarios, the car’s computer may need to relearn voltage patterns or the charging system may require a re-calibration after replacing the auxiliary battery.
Bottom line
The trunk battery on a 2015 Malibu is not universal. It’s most commonly associated with Malibu Eco/eAssist or other specialty configurations where an auxiliary 12V battery supports the hybrid or electrical loads. If your car is not a hybrid and you don’t recall a factory trunk battery option, it could be aftermarket or a feature tied to a specific market or trim. Verify with your VIN, the owner’s manual, or a Chevrolet professional to confirm the exact setup for your vehicle.
Summary
In short, a battery in the trunk of a 2015 Malibu usually signals an auxiliary power source tied to a mild-hybrid or special configuration, but it’s not present on every model. Confirm your trim, check the VIN and manual, and consult a technician if you’re planning maintenance or battery replacement. Understanding the exact layout helps ensure proper care and safe handling of your vehicle’s electrical system.