These instructions apply to the BMW 5 Series Mk4 (E39) 1996-2004.
For other models, please choose your vehicle here.
Disconnecting the 12 V battery on a BMW 5 Series (E39, 1996–2004) is a simple job, but there’s one thing many owners don’t expect: the battery lives in the boot, not the engine bay. There’s no battery registration on this generation. This guide covers the safe order of work and what to reset afterwards.
Where the Battery Is
The battery is in the boot (luggage compartment), behind the right-hand side trim panel. There’s a remote jump-start positive terminal under the bonnet, but the battery itself is in the boot. Open the side panel to reach the terminals.
Before You Disconnect
- Note your radio code and settings.
- Turn the ignition off and remove the key. Close the windows first (so you can still operate them after).
- If working near airbags or seat-belt pretensioners, after disconnecting wait 1 minute before handling those parts.
Disconnecting — Correct Order
- Open the boot and fold back the right-side trim to reach the battery.
- Disconnect the negative (−, earth) terminal first and lift the lead clear.
- Only undo the positive (+) terminal (under its cover) if you are removing the battery completely — release the vent hose first.
Reconnecting — Correct Order
- Refit the battery and secure the hold-down and vent hose.
- Connect the positive (+) lead first, then the negative (−) earth lead last. Tighten both firmly.
- Turn the ignition on for a few seconds before starting.
What to Reset Afterwards
- Enter the radio code and reset the clock and presets.
- If the power windows lose their one-touch/anti-trap, re-teach each one: hold the switch fully up until closed, then hold a moment longer; do the same fully down.
- The diamond key’s rechargeable cell tops up while the key is in the ignition slot — if a key has gone flat from disuse, leave it in position 1 to recharge (see FAQ).
When a Warning Persists
One or two lights right after reconnecting is normal and should clear on a short drive. If a warning stays on, a fault code may be stored — reading it needs an OBD scanner, and you can look up what a BMW code means on autodtcs.com.
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 battery on an E39?
In the boot, behind the right-hand side trim — not the engine bay. Use the under-bonnet jump post only for jump-starting.
Do I need to register a new battery?
No — the E39 predates battery registration. Fit the correct battery and enter the radio code.
Why won’t my key remote work after sitting unused?
The E39 “diamond” key has a rechargeable cell that charges from the ignition slot — it isn’t a coin cell you swap. If it’s flat from disuse, leave the key in the ignition (position 1) to recharge it; a fully dead one takes around 30 hours. A key that won’t hold charge needs replacing by BMW.
How long should I leave it disconnected?
Around 10–15 minutes with the car locked lets the modules power down if you’re resetting electronics.
To clear the service reminder after maintenance, see our BMW 5 Series service indicator reset guide.
Independent guide — not affiliated with BMW. Always follow your official service manual and safety precautions. Read our full disclaimer.