The location varies by model and options, but in 2018 Jeeps with an auxiliary (secondary) battery used for stop‑start or electronic support, the battery is typically either in the engine bay on the passenger side near the firewall or in the rear cargo area beneath the floor panel.
This article explains the typical placements across common 2018 Jeep models and offers practical steps to identify and access the auxiliary battery safely for maintenance or replacement.
Common locations by model (overview)
Note: exact placement depends on trim and regional market. Use these as a starting point to locate the auxiliary battery on a 2018 Jeep.
- Engine bay, passenger side near the firewall: A secondary 12V battery may support electronics when the engine is off or during high electrical demand.
- Rear cargo area under the floor panel: Some configurations place the auxiliary battery in the rear compartment behind the rear seats, accessible by lifting the floor panel.
- Under the driver’s seat or in a discreet under-floor tray: A few configurations use a secondary battery tucked away under seating or in a small tray for space efficiency.
To confirm the exact location for your vehicle, check the owner’s manual diagram or the battery label in the engine bay and cargo area, or contact a Jeep dealer.
How to safely identify and access the auxiliary battery
Follow these steps to safely locate and inspect the auxiliary battery without causing damage or injury.
- Park on level ground, apply the parking brake, and turn off the ignition; wait for all systems to shut down.
- Open the hood and visually inspect the engine bay for a second battery, typically labeled “Aux Battery” or “12V AUX.”
- If you don’t see a second battery in the engine bay, check the rear cargo area: remove the floor panel or trunk mat and look for a sealed battery box behind the rear seats.
- Look for a battery cable with a heavier gauge and a separate grounding strap; the auxiliary battery may have its own fuses in a dedicated fuse box near it.
- Consult the vehicle’s fuse/relay diagram in the owner’s manual to locate any dedicated aux-battery relays or fuses.
- If you’re unsure or the vehicle has special equipment (start-stop, eTorque, or a forced battery disconnection feature), contact a certified Jeep technician for service.
Safety note: Always disconnect the negative terminal first if you must service either battery, and wear eye protection and gloves. Modern Jeeps with dual electrical systems may have capacitors that retain charge; never assume the system is dead.
Model-specific notes (optional)
Wrangler (2018, JL generation)
On 2018 Wrangler JL models equipped with an auxiliary battery, the secondary 12V battery is typically located in the rear cargo area behind the rear seats, beneath a removable floor panel. Always verify with the owner's manual for your exact trim and market, as configurations can vary by option group.
Grand Cherokee (2018)
Grand Cherokee models built with stop-start or eTorque may place the auxiliary battery in the engine bay on the passenger side or use a rear-area installation depending on the drivetrain and options. Check the manual diagrams for the precise location on your vehicle.
If your Jeep isn’t one of these configurations, the general rule remains: the auxiliary battery is designed to be out of the way, either in the engine bay or in the cargo area, and its primary purpose is to power electronics when the engine is off or during high-demand events.
Summary
In 2018 Jeeps, the auxiliary battery location is not universal. Start by checking the engine bay on the passenger side near the firewall, then inspect the rear cargo area under the floor panel if no second battery is visible. Consult your owner’s manual diagrams or a dealer for an exact location, and always follow safety procedures when inspecting or replacing a battery.