Disconnect and Reconnect the Battery

Disconnecting the 12 V battery on a Hyundai Bayon (2021–present) is a simple engine-bay job, and a handy one to get right whether you are fitting a new battery, doing electrical work, laying the car up over winter, or bringing it back after a flat. This guide covers safe disconnection and exactly what the car needs re-taught once the power is back, so nothing surprises you afterwards.

Where the Battery Is

The 12 V battery sits in the engine bay, behind a cover. The petrol and 48V mild-hybrid Bayon keep the 12 V battery here — only the small 48V unit on the mild-hybrid is a specialist item.

Lift the cover and identify the two terminals before you touch anything: the negative (−) earth usually sits under a black cap and grounds to the body, while the positive (+) is under a red cap and feeds the car’s supply. On the mild-hybrid, leave the separate 48V unit alone — the ordinary 12 V battery is all an owner needs to touch here.

Before You Start

• Make sure the ignition is fully off and the dash is dark, not in accessory mode.
• Take the smart key out of range so the car can’t wake and power a circuit while you work.
• Switch off the lights, climate and any accessories so nothing is drawing current at the moment you disconnect.
• Give it a minute or two after locking up for the electronics to sleep.
• Have the right spanner ready and wear gloves and eye protection.

Disconnecting

1. Switch the ignition off, remove the smart key and wait a minute for the electronics to sleep.
2. Disconnect the negative (−) terminal first, ease the lead off the post and tuck it aside so it can’t spring back onto the terminal.
3. If removing the battery, disconnect the positive (+) next, then release the clamp and lift the battery out level.

Reconnecting & Re-teaching

1. Reconnect positive (+) first, then negative (−) last, and check both clamps are tight before refitting the cover.
2. Reset the clock; the radio usually reloads on its own.
3. Re-initialise the one-touch windows — the auto-up and anti-pinch travel is the thing owners most often notice missing. See our Bayon window guide.
4. If your car has a sunroof, it may also need re-initialising.
5. Take a short drive so the engine settles and any warning light left over can self-clear.

The Bayon doesn’t need the battery coded — a like-for-like replacement simply goes in.

If a Warning Light Stays On

• Check both clamps are properly tight — a loose earth causes most odd behaviour after a disconnect.
• Let the car relearn over a short drive before deciding something is wrong.
• If the windows still won’t auto-close, run the re-initialise again from the start.
• If the car won’t hold charge, the battery itself may simply be worn out.
• Read any code that lingers rather than clearing it blind.

Frequently Asked Questions

Where is the battery on the Hyundai Bayon?

The 12 V battery is in the engine bay behind a cover, on both the petrol and 48V mild-hybrid. Only the separate small 48V unit on the mild-hybrid is a specialist part — you leave that one alone.

Which terminal first on the Bayon?

The negative (−) first, and reconnect it last. Taking the earth off first stops a spanner shorting the battery against the bodywork while you work.

Does the Hyundai Bayon battery need coding?

No — just fit it and re-teach the windows (and sunroof if fitted). A like-for-like 12 V battery doesn’t need coding on the Bayon.

Will I lose my radio?

No code is normally needed — just reset the clock and the radio reloads on its own once power is back.

What do I need to reset afterwards?

Reset the clock, re-initialise the one-touch windows, and re-teach the sunroof if fitted. Any warning light left over usually clears after a short drive.

Why won’t my windows auto-close now?

The power cut cleared their learned position, so the auto-up and anti-pinch function drops out. Run the quick re-initialise from the window guide and they come straight back.

For any warning light that stays on, look up the code on autodtcs.com. To clear the service reminder, see our Bayon service reset.