12-volt battery replacement

Assembly

1. 01

   Identify the cables and put the car to sleep

   Ignition off, keys out, doors closed. On many late cars, wait a few minutes so modules go to sleep. Find NEG (−, usually black) and POS (+, usually red, often a cover). If the battery is not in the engine bay (trunk, under seat), confirm you are on the 12V service battery, not an HV service disconnect.

   If you see orange high-voltage cables, stop. That is not this job.

   
2. 02

   Negative first, then positive

   Loosen the negative clamp and twist it off the post. Tuck it aside so it cannot spring back. Then remove the positive. Undo the hold-down. Lift the battery out with two hands — it is heavier than it looks. Do not tip a flooded battery.

   Never pry on a post with a screwdriver through both terminals.

3. 03

   Tray, posts, and the new unit

   Clean the tray and the cable clamps until the metal is bright. Set the new battery with the posts matching the cable reach — do not stretch a cable to the wrong post. Install the hold-down so the case cannot rock. Connect positive first, then negative. The negative last connection is the one that can spark — keep it away from the positive post.

4. 04

   Start and settle the electronics

   Start the engine. Confirm the charge warning is out. Set the clock and windows if they forgot themselves. Some cars want a few minutes of idle or a short drive for the charging system to see the new battery. Register the battery if the manufacturer requires it (many BMWs, some European cars) — otherwise the car will undercharge an AGM.

   If the new battery was not required to be registered and the car still shows a battery warning after a drive, stop guessing and scan it.

Verify every torque and fluid spec against the factory manual for this VIN. Autobay Book is a research assistant, not a substitute for a procedure written for your car.