Disconnect and Reconnect the Battery

Unlike the rear-wheel-drive BMWs that hide the battery in the boot, the BMW 1 Series Mk3 (F40, 2019–present) is front-wheel drive and keeps its 12 V battery in the engine bay. You might disconnect it to renew the battery, to isolate the power for electrical or bodywork repairs, before a long lay-up, or after a jump-start. The one thing that’s the same as every modern BMW: a new battery should be registered with the car’s power-management system. Simply taking the same battery off and putting it back doesn’t need that step — but a swap does, and this guide covers both the safe disconnection and the registration.

Where the 12 V Battery Is

The 12 V battery is in the engine compartment, under a cover — the F40 shares its front-drive platform with the MINI and 2 Series Active Tourer, which is why the battery lives up front rather than in the boot. Lift the cover and you’ll find the negative (−) terminal in black and the positive (+) under a red flap. Most F40s use an AGM battery, which matters when it comes to replacement.

First, a Few Checks

• Switch the ignition fully off and keep the keyless fob out of range so nothing wakes.
• Turn off the lights, climate and radio, and close the doors and boot.
• Note the clock and any personalised settings before power comes off.
• Give the modules a couple of minutes to power down before touching the terminals.
• Have the correct spanner ready, plus gloves and eye protection — and, if you’re fitting a new battery, the means to register it (BMW diagnostics or a compatible independent tool/app).

Disconnecting

1. Switch the car off and remove the key (or keep a keyless fob out of range).
2. Open the bonnet and lift the battery cover.
3. Loosen the negative (−, black) terminal first and lift the lead clear, tucking it aside so it can’t spring back.
4. If you’re removing the battery, loosen the positive (+, red) next, then release the hold-down clamp and lift the battery out level.

Airbag/pretensioner safety: if you’ll be near airbags or seat-belt pretensioners, wait 1 minute after disconnecting the negative before continuing.

Reconnecting & Registering

1. Reconnect positive (+) first, then negative (−) last; tighten both clamps and refit the cover.
2. Reset the clock and date — the on-board clock stops while the car is disconnected.
3. Register a new battery in the power-management system with BMW diagnostics (a dealer, or an independent with the right software or app) so the car charges it correctly and start/stop keeps working. A straight disconnect and reconnect of the same battery doesn’t need this.

Replace AGM with AGM — don’t fit a standard flooded battery, or the charging strategy and start/stop won’t behave. Re-check your one-touch windows too; they can lose their learned end-stops after a power cut and may need a quick re-initialise.

If a Warning Light Stays On or the Car Feels Off

• Check both terminal clamps are properly tight — a loose earth throws up all sorts of spurious warnings.
• If a new battery isn’t registered, start/stop may stay disabled and a charging-related message can appear until it’s done.
• Take a short drive; many messages self-clear after a few normal cycles.
• Re-do the window re-initialise if auto-up hasn’t returned.
• Rule out a genuinely flat or aged battery, and read any code that stays stored.

Registering or Coding the New Battery

Yes. This car has a battery-monitoring system, so a replacement battery must be registered — the car needs to know it is new, or it under-charges it and the fault stays logged. Registration is done through the OBD port with a compatible diagnostic tool (a specialist or dealer, or a capable aftermarket scanner); there is no owner button sequence. Replace like-for-like (AGM for AGM, EFB for EFB).

Frequently Asked Questions

Where is the 1 Series F40 battery?

In the engine bay, under a cover. The F40 is front-wheel drive, so — unlike the rear-drive 3 Series — the battery isn’t in the boot. Lift the cover to reach the negative (−) and positive (+) terminals.

Do I have to register a new battery?

Yes — BMW’s charging strategy needs a new battery registered, or it won’t be charged correctly and start/stop may stop working. Reconnecting the same battery doesn’t need registration.

Which terminal comes off first?

Disconnect the negative (−) first and reconnect it last. That keeps your spanner from shorting a live positive against the bodywork.

Can I fit a normal (non-AGM) battery?

No — replace AGM with AGM to match the F40’s charging strategy and keep start/stop working. A standard flooded battery isn’t a like-for-like swap here.

What do I need to reset afterwards?

The clock and date, and your one-touch windows if auto-up drops out. A new battery also needs registering. Most other messages clear themselves once you’ve driven a short distance.

Will disconnecting reset the service light?

No — the service reminder is a separate procedure and won’t clear just from a battery disconnect. A genuine stored fault will also return until it’s properly fixed.

For any warning light that stays on, look up the code on autodtcs.com. To clear the service reminder, see our 1 Series F40 service reset guide.