Disconnect and Reconnect the Battery

The Honda Jazz Mk4 (GR, 2020–present) is an e:HEV hybrid, so it carries two batteries: a high-voltage traction battery (never touch it) and a small 12 V battery that runs the electronics, lighting and the systems that wake the car up. This guide covers safely disconnecting the 12 V battery — the one you change or isolate for electrical work, long storage, or after a flat. Done in the right order the Jazz relearns cleanly; you only have a couple of small things to reset afterwards. The high-voltage side stays sealed and is strictly workshop territory.

Important: Which Battery This Is

You only ever work on the 12 V battery. Never touch the orange high-voltage cables or the traction battery — that system holds a dangerous voltage and is for trained technicians only. The 12 V job below is completely owner-safe: it’s the same kind of battery, terminals and spanner you’d find on any small petrol car.

Where the 12 V Battery Is

On the Jazz e:HEV the 12 V battery is in the engine compartment, under a cover. Lift the cover and you’ll find the two terminals: negative (−) on the black lead and positive (+) on the red lead, usually with a protective flap. Identify both before you start so there’s no doubt which one you’re loosening.

Getting Ready

• Switch the car fully off — not in READY — and close the doors, lights, climate and boot.
• Take the smart key well away from the car so it can’t re-wake a module while you work.
• Note your radio presets and clock so you can restore them quickly.
• Wait a couple of minutes after switching off for the control units to power down.
• Have the right spanner (usually a 10 mm nut) plus gloves and eye protection to hand.

Disconnecting

1. Switch the car fully off (not “ready”) and keep the smart key away from the car.
2. Wait about 3 minutes after switching off so the control units and any airbag/pretensioner circuits power down.
3. Loosen and disconnect the negative (−, black) terminal first, then lift the lead clear and secure it so it can’t fall back.
4. If you’re removing the battery, disconnect the positive (+, red) next, then undo the hold-down and lift the battery out.

Airbag/pretensioner safety: if you’ll be near airbags or seat-belt pretensioners, allow the system to discharge for the full few minutes first.

Reconnecting

1. Refit the battery and hold-down, then reconnect positive (+) first and negative (−) last; tighten both and refit the cover.
2. Reset the clock and re-enter your radio presets.
3. The engine may idle a touch rough at first — that settles over the first few miles as the car relearns.
4. Recalibrate the tyre-pressure (deflation) monitor once tyres are set correctly — see our Jazz Mk4 TPMS guide.
5. If the service reminder needs clearing, follow our Jazz Mk4 service reset guide.

A like-for-like 12 V battery does not need coding or registering on the Jazz — reset the clock and recalibrate the deflation monitor and you’re done.

If a Warning Light Stays On or the Car Feels Off

• Recheck both terminals are clean and properly tight — a loose clamp is the usual cause of odd behaviour after a disconnect.
• Let the Jazz relearn over a gentle 10–15 minute drive; several lights self-clear once systems see normal running.
• If the deflation warning stays on, re-run the tyre-pressure calibration with the tyres set correctly.
• If it was slow to wake or died again quickly, the 12 V battery itself may simply be flat or worn out.
• Any code that won’t clear on its own can be read and looked up so you know what it means.

Frequently Asked Questions

Where is the 12 V battery on the Jazz hybrid?

In the engine compartment, under a cover. It’s an ordinary small 12 V battery with black negative and red positive terminals — nothing to do with the high-voltage traction battery, which is separate and sealed.

Is it safe to disconnect the 12 V battery on the hybrid?

Yes — the 12 V system is isolated from the high-voltage side, so the job is owner-safe. Just leave the orange cables and the traction battery completely alone and work only on the 12 V terminals.

Which terminal do I disconnect first?

Disconnect the negative (−) first and reconnect it last. That keeps a slipped spanner from bridging the positive post to the body and causing a short.

What do I have to reset afterwards?

The clock and radio presets, a short idle relearn that happens as you drive, and the tyre-pressure deflation monitor. Comfort settings may want a quick check too. None of it needs a workshop.

Does a new 12 V battery need coding?

No — a like-for-like 12 V battery needs no coding or registration on the Jazz. Fit it, reconnect in the right order, reset the clock and recalibrate the deflation monitor.

Can I jump-start it instead of disconnecting?

If the 12 V battery is simply flat you can jump-start the Jazz from its 12 V terminals rather than pull the battery. But if it keeps going flat, the battery is worn and disconnecting to renew it is the real fix.

For any warning light that stays on after the job, look up the code on autodtcs.com so you know exactly what it’s telling you.