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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: Smart Key Diagnostic
Repair procedures Inspection 1. In the body electrical system, failure can be quickly diagnosed by using the vehicle diagnostic system (KDS). The diagnostic system (KDS) provides the following information. (1) Self diagnosis : Checking failure and code number (DTC). (2) Current data : Checking the system input/output data state.Kia Stinger (CK) 2018-2023 Owner's Manual: Timing Chain Cover
Repair procedures Removal In case of removing the high pressure fuel pump, high pressure fuel pipe, delivery pipe, and injector, there may be injury caused by leakage of the high pressure fuel. So don’t do any repair work right after engine stops. • Use fender covers to avoid damaging painted surfaces.