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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: ECS-G Sensor
Repair procedures Removal [Body G Sensor] Front 1. Turn ignition switch OFF and disconnect the negative (-) battery cable. 2. Remove wheel nuts, wheel and tire (A) from hub. Tightening torque: 107.9 - 127.5 N·m (11.0 - 13.0 kgf·m, 79.6 - 94.0 lb·ft) Be careful not to damage the wheel bolts when removing the wheel and tire (A).Kia Stinger (CK) 2018-2023 Owner's Manual: Releasing the parking brake
To release the EPB (electronic parking brake), press the EPB switch while doing the following: Have the ignition switch or engine start/stop button in the ON position. Depress the brake pedal. The shift lever must be in P (Park). Make sure the brake warning light goes off. To release EPB (electronic parking brake) automatically: Shift lever in P (Park) With the engine running depress the brake pedal and shift out of P (Park) to R (Reverse) or D (Drive).