Disconnect and Reconnect the Battery

Last updated: June 12, 2026

Disconnecting the 12 V battery on a Hyundai i20 Mk2 (GB, 2014–2020) is a simple job, but the car loses a few settings while the power is off and needs a couple of quick re-initialisations afterwards — the windows, and on start/stop cars the auto stop/start function. This guide gives the safe order of work and what to reset once the leads are back on.

Where the Battery Is

The battery sits in the engine bay under a plastic cover. Lift the cover to reach the two clamps. Cars with Hyundai’s ISG (Idle Stop & Go) start/stop system use an uprated AGM/EFB battery — replace like-for-like, as a standard battery will not survive the stop/start cycling.

Before You Disconnect

• Note your preset radio stations and user preferences — they are wiped when the power goes.
• Make sure the ignition key is in the OFF position (and any keyless fob is away from the car) before you touch the terminals.
• If you want to keep settings alive, plug in a memory-saver. The steps below assume you are not using one.
• If you will work 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 straight away. Turn the ignition on for a few seconds first so the modules wake up.

What to Reset Afterwards

• Reset the date and time, and re-enter your radio presets and user preferences.
• Re-initialise the electric windows — the one-touch/auto-up function is lost until you re-teach it. With the ignition on, hold the window switch fully up for a couple of seconds after the glass seats, then release; repeat for each window.
• Re-initialise the electric sunroof if fitted, using the roof switch.
• Let the ISG (start/stop) system re-initialise. After a power loss the auto stop/start may not work until the car has been driven and the battery sensor relearns the state of charge — a short drive normally restores it.

If a Warning Light Stays On

A light or two 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 i20 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.

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 will allow auto-stop. Drive the car normally for a while and it should return; a freshly fitted battery may need registering on ISG models.

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 electrical 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 i20?

On ISG/start-stop cars it is best to register a new AGM/EFB battery with a Hyundai-capable tool so the charging system manages it correctly. Non-ISG cars are less fussy.

To clear the service reminder after maintenance, see our Hyundai i20 Mk2 service indicator reset guide.