Disconnect and Reconnect the Battery

Disconnecting the 12 V battery on your Alpina B5 / D5 (G30/G31, 2017–2024) is a job most owners can do at home. You’ll want to pull the terminals for a battery renewal, before a long winter lay-up, when you’re doing electrical or bodywork near the airbags and pretensioners, or to bring a car back to life after a deep discharge. The B5 and D5 are built on the BMW 5-Series (G30 saloon / G31 Touring), so the layout follows that platform closely — and, as on those cars, the battery lives in the boot rather than the engine bay. Done in the right order and given a moment to relearn, the car settles back to normal without drama.

Where the 12 V Battery Is

The 12 V battery is in the luggage compartment (boot), on the right-hand side under the floor trim. Lift the boot floor panel and fold back the side trim to expose it; on the Touring you may need to release a couple of turn-fasteners first. You’re looking for two clamped terminals — the negative (−) is the earth/ground lead and is usually the black one, while the positive (+) is red and often sits under a plastic cover. Take a second to identify both clearly before you touch a spanner to either, as the positive stud in the boot is also the jump-start point.

Before You Start

• Switch the ignition fully off, take the key fob well away from the car, and let it lock down.
• Turn off the lights, climate, and anything plugged into a 12 V socket so there’s no load on the system.
• Note your radio presets and any personal settings — the clock stops and presets can drop when the battery is disconnected.
• Wait a couple of minutes after switching off so the control modules power down and go to sleep.
• Have the correct spanner ready (the terminals are usually a 10 mm nut), plus gloves and eye protection.

Find the Battery First

Disconnecting Safely

1. Confirm the ignition is off and open the boot floor to reach the battery.
2. Slacken and remove the negative (−) terminal first, then tuck the cable aside so it can’t spring back onto the post.
3. Only then loosen and lift off the positive (+) terminal.
4. If you’re working near the airbags or seat-belt pretensioners, wait a few minutes after disconnecting before you start.

Reconnecting and Re-initialising

Reverse the order: fit the positive (+) first, then the negative (−) last, and tighten both clamps so they’re secure but not over-torqued. Once power is restored, a few things need settling:

• Clock and radio — re-enter the time and any presets that dropped.
• Power windows — re-initialise the one-touch/anti-pinch by holding each switch fully up at the top limit, then fully down, for a moment.
• Tyre pressure monitor — re-run the TPMS reset from the iDrive menu once you’re ready to drive.
• The condition-based service (CBS) data is retained, so your service reminders should carry over.

If Something Isn’t Right Afterwards

• Check both clamps are tight and fully seated — a loose earth is the usual cause of odd electrical behaviour.
• Take the car for a short drive; many warning lights self-clear once the modules see everything working normally.
• If a window still doesn’t auto-close, repeat the hold-at-the-limits relearn.
• Fit a like-for-like AGM battery of the correct rating; on BMW-based cars registration is recommended, though the car will run with a correctly matched replacement.
• If a light stays on, it has stored a code — look it up on autodtcs.com.

Frequently Asked Questions

Where is the battery on an Alpina B5/D5?

In the luggage compartment (boot), on the right-hand side under the floor trim — not in the engine bay. That mirrors the BMW G30/G31 5-Series it’s built on, which also carries the battery in the boot.

Which terminal do I disconnect first?

Always the negative (−) earth terminal first, and reconnect it last. That order removes the ground path before you touch the positive, which keeps you from shorting a spanner against the bodywork.

What will I need to reset afterwards?

Mainly the clock and radio presets, the one-touch window function, and the tyre-pressure monitor. The CBS service data is retained. A short drive lets the car relearn and clears most transient warnings.

Does a new battery need coding on an Alpina B5/D5?

A like-for-like AGM battery is what the car expects. Registering the new battery to the vehicle is recommended so the charging system manages it correctly, but the car will start and run with a correctly matched replacement.

Will disconnecting the battery clear fault codes or the service light?

It can clear some temporary stored codes, but it isn’t a proper fix — a genuine fault will simply set the code again. The condition-based service data is stored separately and isn’t reset by pulling the battery.

Can I jump-start it instead of disconnecting?

Yes — there’s a positive jump-start terminal in the engine bay for that. Disconnecting is only needed for a renewal, storage, or work near the airbags; for a flat battery a jump or a proper charge is usually the quicker route.

To relearn the windows, hold each switch at its upper and lower limits for a moment. If a warning light stays on after everything’s reconnected, decode it on autodtcs.com.