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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: Fluid (ATF)
Repair procedures Automatic Transmission Fluid (ATF) Level Check 1. Start the engine to warm up the ATF. Do not step on the brake and accelerator simultaneously to warm up the ATF. 2.Kia Stinger (CK) 2018-2023 Owner's Manual: For best battery service
Keep the battery securely mounted. Keep the battery top clean and dry. Keep the terminals and connections clean, tight, and coated with petroleum jelly or terminal grease. Rinse any spilled electrolyte from the battery immediately with a solution of water and baking soda. If the vehicle is not going to be used for an extended time, disconnect the battery cables.