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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: Field Effect Transistor (DATC)
Repair procedures Inspection 1. Turn the ignition switch ON. 2. Manually operate the control switch and measure the voltage of the blower motor. 3. Operate the control switch to raise the voltage up to high speed. Specification Fan Speed Manual Control Auto Control 1 4.Kia Stinger (CK) 2018-2023 Owner's Manual: Line Pressure Control Solenoid Valve (LINE_VFS)
Specifications Specifications Item Specification Control type N/L (Normal Low) Control pressure kpa (kgf/cm², psi) 0 - 519.75 (0 - 5.3, 0 - 75.38) Current (mA) 0 - 850 Coil resistance (Ω) 5.