Disconnect and Reconnect the Battery

Last updated: June 4, 2026

Disconnecting the 12 V battery on a Hyundai i30 Mk2 (GD, 2012–2017) is a routine job, but the car loses several settings while the power is off — the clock, radio presets, climate and trip-computer settings, and the one-touch windows — so it pays to do it in the right order and run the quick re-initialisations afterwards. This guide covers the safe sequence and the resets the i30 needs.

Where the Battery Is

The battery is in the engine compartment under a plastic cover. Lift the cover to reach the clamps. Cars with ISG (Idle Stop & Go) start/stop use an uprated AGM/EFB battery — replace like-for-like, because a standard battery will not cope with the stop/start cycling.

Before You Disconnect

• Check your audio system security code — some i30 head units lock after a power loss and ask for it.
• Note your radio presets and user preferences, which are wiped when the power goes.
• Make sure the ignition key is OFF and all electrical consumers are switched off before touching the terminals.
• If you want to keep settings alive, plug in a memory-saver. The steps below assume you are not.
• If working near airbags or seat-belt pretensioners, disconnect the battery and wait at least 3 minutes before handling those parts.

Disconnecting — Correct Order

1. Turn the ignition off and remove the key.
2. Open the bonnet and lift off the battery cover.
3. Slacken the negative (−, earth) terminal first and lift the lead clear, tucking it aside.
4. Only undo the positive (+) terminal if you are removing the battery completely.
5. If removing the battery, undo the base clamp and lift it out upright.

Reconnecting — Correct Order

1. Refit the battery and secure the hold-down clamp.
2. Connect the positive (+) lead first, then the negative (−) earth lead last. Tighten both firmly.
3. Do not start the engine immediately. Turn the ignition on for a few seconds first.

What to Reset Afterwards

• Enter the radio code if asked, and reset the date and time.
• Re-enter your radio presets and user preferences.
• Re-initialise the climate control — the electronic climate unit may need a moment to recalibrate; running it through its range helps.
• Reset the trip-computer settings (units, average figures) as preferred.
• Re-initialise the electric windows — see the quick steps below or the dedicated guide.
• Re-initialise the electric sunroof if fitted.

Quick Window Re-initialisation

1. Turn the ignition on.
2. Pull and hold the window close switch until the window is fully shut, then wait 1 second before releasing.
3. Repeat for the passenger window (and rears).

Full detail is in our i30 Mk2 electric window reinitialisation guide.

If a Warning Light Stays On

One or two lights right after reconnecting is normal and should clear on a short drive. If the airbag, ABS or engine light remains, a fault code was logged during the power interruption. Reading it needs an OBD scanner — you can look up what an i30 code means on our sister site autodtcs.com.

Tools You Need

• 10 mm spanner/socket for the terminal clamps and hold-down.
• Optional memory-saver to preserve presets and settings.
• Your radio keycode, if the head unit is code-protected.

Frequently Asked Questions

Why doesn’t my start/stop work after reconnecting the battery?

Hyundai’s ISG needs the battery sensor to relearn the state of charge before it allows auto-stop. Drive normally for a while and it should return; a new battery may need registering on ISG cars.

How long should I leave it disconnected to reset the electronics?

About 15 minutes with the doors shut lets the modules power down fully, clearing most transient glitches.

Why won’t my windows auto-close after reconnecting?

That is expected — the one-touch function disables itself after a power loss. Re-initialise each window and it returns.

Do I need to register a new battery on an i30?

On ISG/start-stop cars, yes — register a new AGM/EFB battery with a Hyundai-capable tool so the charging system manages it correctly.

To clear the service reminder after maintenance, see our Hyundai i30 Mk2 service indicator reset guide.