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The battery is in the trunk under the compartment cover.
When replacing the battery, disconnect the negative (-) cable (1) and remove the positive (+) battery fuse box (2).
Remove the battery mounting bracket (3).
WARNING - Touching metal surfaces in the trunk under the compartment cover

Do not touch metal surfaces in the trunk under the compartment cover while the engine is operating or hot. Doing so could result in serious personal injury. Turn the engine off and wait until it cools down or wear gloves to replace the battery from the luggage room.
Your vehicle has a maintenance-free, calcium-based battery.
When recharging the battery, observe the following precautions:
Reset items
Items should be reset after the battery has been discharged or the battery has been disconnected.
Kia Stinger (CK) 2018-2023 Owner's Manual: Filler-Neck Assembly
Repair procedures Removal 1. Switch "OFF" the ignition and disconnect the negative (-) battery terminal. 2. Remove the fuel filler cap after opening the fuel filler door. 3. Lift the vehicle. 4. Remove the rear-left wheel & tire and wheel house cover.Kia Stinger (CK) 2018-2023 Owner's Manual: SS-A Solenoid Valve (ON/OFF)
Specifications Specifications Item Specification Control type ON/OFF Control pressure kpa (kgf/cm², psi) 539.36 (5.5, 78.23) Current (mA) 0 - 600 Coil resistance (Ω) 10.5 ± 0.5 Components and components location Components Location 1.