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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: Main components of the occupant detection system
An detection device located within the front passenger seat cushion. An electronic system which determines whether the passenger air bag systems should be activated or deactivated. An indicator light located on the instrument panel which illuminates the words PASSENGER AIR BAG “OFF” indicates the front passenger air bag system is deactivated.Kia Stinger (CK) 2018-2023 Owner's Manual: D Position 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.