Disconnect and Reconnect the Battery

Disconnecting the 12 V battery on your Alfa Romeo 147 (2000–2011) is a straightforward driveway job, and one worth doing carefully whenever you fit a new battery, store the car over winter, or work near the airbags and seat-belt pretensioners. The 937-series 147 is an older, relatively simple car electrically compared with Alfa’s later models, which actually makes the battery job easier — there is no isolator to hunt for and no factory tool needed. Provided you take the terminals off and put them back in the right order, the 147 powers down and wakes up cleanly, relearning the few settings it forgets over the first short drive. A single spanner and a methodical approach are all it takes.

Where the 12 V Battery Is

The 147 carries its 12 V battery in the engine compartment, in the usual front corner under a cover. Raise the bonnet, unclip or lift the cover away, and the two terminal posts are on top of the battery. The negative post is marked with a minus (−) symbol and takes the black lead; the positive post carries a plus (+) symbol, a red lead, and typically a protective flap. Make sure you can tell the two apart before you pick up a spanner — the whole procedure depends on removing and refitting them in the right sequence.

Before You Start

• Turn the ignition fully off and take the key out of the car so nothing wakes the electronics mid-job.
• Switch off the lights, blower, radio and any other accessories.
• Note your radio security code — older 147s with a coded radio need it re-entered — along with your station presets.
• Allow a couple of minutes after switching off for the modules to power down, and a little longer before working near the airbags.
• Wear gloves and eye protection, and have the correct spanner — usually 10 mm — ready before you begin.

Find the Battery First

Disconnecting the Battery

1. Confirm the ignition is off and everything electrical is switched off.
2. Loosen the clamp nut on the negative (−) terminal first, ease the lead off the post and set it aside so it cannot fall back.
3. Now loosen and remove the positive (+) terminal, lifting off its protective cover first.
4. If you will be working near the airbags or pretensioners, wait a few minutes after disconnecting before starting.

Reconnecting the Battery

1. Fit the positive (+) terminal first, seat the clamp fully and tighten it, then refit the protective cover.
2. Connect the negative (−) terminal last and tighten its clamp.
3. Check both clamps are firm — a loose terminal is the usual reason for strange electrical behaviour afterwards.

What You’ll Need to Reset Afterwards

The 147 loses only a few stored settings with the battery off, and puts most of them back on its own once power returns and you take a short drive:

• Clock and radio — re-enter the time, your presets, and the security code on cars with a coded head unit.
• Electric windows — if the one-touch stops working, hold each switch fully up until the glass closes and pause a moment to re-teach the end stop.
• Electric sunroof (if fitted) relearns its travel — run it fully closed and hold the switch to re-initialise.
• Any temporary warning lights generally clear after the car has completed a short run.

If a Warning Light Stays On or the Car Feels Off

• Re-check that both clamps are tight and properly seated on their posts.
• Let the car relearn over a gentle five-to-ten-minute drive before deciding anything is wrong.
• Repeat the window one-touch relearn if the glass will not auto-close.
• Rule out a genuinely flat or aged battery — a tired one can drop voltage as soon as it is loaded.
• If a light will not go out, it has stored a code you can read and look up.

Frequently Asked Questions

Where is the battery on an Alfa Romeo 147?

In the engine compartment, in the usual front corner under a cover. Lift the bonnet and remove the cover to reach the two terminal posts on top.

Which terminal do I take off first?

Take the negative (−) terminal off first. When reconnecting, reverse it: positive (+) on first, then the negative last, and tighten both clamps.

What do I need to reset after disconnecting the 147 battery?

Re-enter the clock, radio presets and the security code on cars with a coded radio, and re-initialise the one-touch windows and sunroof if they stop working after power returns.

Does a new battery need coding on a 147?

No. A like-for-like replacement of the correct capacity needs no coding on the 147 — you simply re-enter the settings above. Just fit a battery that matches the original specification.

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

It can clear some temporary codes, but a real fault will set its light again once the car sees the problem. It does not reset the scheduled service reminder, which is a separate procedure.

Can I jump-start the 147 instead of disconnecting the battery?

Yes — if the battery is only flat, a jump-start will get you moving without removing it. You only need to disconnect the battery for renewal, storage, or work that requires the electrics to be dead.

If a warning light stays on after reconnecting, note the code and look it up on autodtcs.com.