Disconnect and Reconnect the Battery

Reviewed by the Service Reset editor · Updated August 22, 2026 · How we verify
Quick referenceTools10 mm spannerTime~15 minMethodDisconnect negative terminal first

These instructions apply to the Ford Puma Mk2 (J2K) 2020-Present.
For other models, please choose your vehicle here.

Disconnecting a battery on the Ford Puma (2020–present) is mostly a normal 12 V job — but the popular EcoBoost mHEV versions add a twist: they carry a 48 V mild-hybrid battery as well, in a different place, and that one isn’t an owner part. This guide keeps the two clearly apart so you work on the right battery safely, and covers the BMS reset a new 12 V needs.

Ford Puma Mk2 — the vehicle covered in this guide.
Ford Puma Mk2. Photo by Alexander Migl via Wikimedia Commons, licensed CC BY-SA 4.0.

Two Batteries on the mHEV — Know Which Is Which

  • 12 V starter battery (every Puma) — in the engine bay, under a cover. This is the one you disconnect or replace for normal electrical work, jump-starts and flat-battery problems.
  • 48 V lithium battery (mHEV only) — located under the front passenger seat, under a carpet flap. It feeds the belt-driven starter-generator. Leave it alone: the 48 V system must be properly deactivated first, which is workshop territory, not a driveway job.

For the rest of this guide, “the battery” means the 12 V in the engine bay.

Disconnecting the 12V Battery

  1. Apply the parking brake, switch the ignition off, and make sure all electrical consumers (lights, climate, radio) are off.
  2. Wait 2 minutes for the modules to power down.
  3. Open the bonnet and disconnect the earth/negative (−) cable first, then the positive (+) if you’re removing the battery.

Working near airbags or pretensioners as well? Keep the ignition off and leave the system to discharge before going near pyrotechnic parts.

Reconnecting and What to Re-set

  1. Reconnect positive (+) first, then earth/negative (−) last; tighten and refit the cover.
  2. Reset the clock and date, and re-enter radio presets and personal settings.
  3. Re-initialise the power windows — one-touch drops out after a power cut. See our Puma window initialise guide.

Fitted a New Battery? Reset the BMS

The Puma uses a Battery Monitoring System (BMS) for smart charging and to manage start/stop. When you fit a new 12 V battery, the BMS should be told, so it charges the fresh battery correctly and re-enables Auto Start-Stop. On the Puma this is done with Ford’s diagnostic software (a dealer or an independent with FDRS/Forscan) — a like-for-like swap will run without it, but start/stop and charging behave better once it’s reset. A simple disconnect/reconnect of the same battery doesn’t need it.

Frequently Asked Questions

Is the Ford Puma a 48V mild hybrid?

The EcoBoost mHEV versions are — they have a genuine 48 V system and a 48 V battery under the passenger seat. Plain (non-mHEV) EcoBoost and the diesel use only the 12 V battery.

Where is the 12V battery on the Puma?

In the engine bay under a cover — the same place on every Puma, mHEV or not. The under-seat battery is the separate 48 V unit.

Can I touch the 48V battery myself?

No — the 48 V system has to be deactivated properly before anyone works on it. Treat it as a workshop item; only the engine-bay 12 V is owner-serviceable.

Why won’t Auto Start-Stop work after a new battery?

The BMS needs resetting so it trusts the new battery’s charge state; until then (or until the battery is fully charged) start/stop may stay off.

For any warning light that stays on, look up the code on autodtcs.com. To clear the oil-service reminder afterwards, see our Puma service reset guide.

Independent guide — not affiliated with Ford. Always follow your official service manual and safety precautions. Read our full disclaimer.

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