Disconnect and Reconnect the Battery

Last updated: June 12, 2026

Disconnecting the 12 V battery on a Hyundai Tucson Mk3 (TL, 2015–2020) is a routine job, but the car loses several settings when the power goes and needs a handful of quick re-initialisations afterwards — the windows, the sunroof, the power tailgate and, on start/stop cars, the ISG system. This guide covers the safe order of work and what to reset once the leads are back on.

Where the Battery Is

The battery is in the engine bay. Lift any cover to reach the two clamps. Cars with ISG (Idle Stop & Go) start/stop use an uprated AGM/EFB battery — replace like-for-like.

Before You Disconnect

• Note your radio presets and user preferences.
• Make sure the ignition key is OFF and remove it (or keep the smart key away from the car).
• 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 reach the battery.
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. Turn the ignition on for a few seconds before starting the engine.

What to Reset Afterwards

• Reset the date and time and re-enter radio presets and user preferences.
• Re-initialise the electric windows — see our Tucson window guide.
• Re-initialise the sunroof if fitted — see our Tucson sunroof guide.
• Re-initialise the power tailgate if it stops opening/closing automatically — see our Tucson power tailgate guide.
• Let the ISG (start/stop) re-initialise over a drive on a healthy battery; a new battery should be registered.

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. Reading it needs an OBD scanner — you can look up what a Tucson 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 settings.

Frequently Asked Questions

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

Hyundai’s ISG needs the battery sensor to relearn the state of charge; drive normally for a while and it returns. A new battery should be registered with a Hyundai-capable tool.

Why won’t my power tailgate work after the battery was off?

It loses its calibration during a power loss — re-initialise it as in our tailgate guide and it returns.

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

Around 15 minutes with the doors shut lets the modules power down fully.

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

Expected — the one-touch disables itself after a power loss. Re-initialise each window and it returns.

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