RollingMechanics

Batteries & starting

Mobile car battery replacement

A car that won't turn over is the most common reason people call a mobile mechanic — and it isn't always the battery. Starting faults can come from the battery, the alternator, the starter motor, the earth straps or a parasitic drain quietly flattening the car overnight.

We arrange mobile battery testing and replacement across London and anywhere inside the M25, and a little beyond if you ask. If the battery is fine, you'll be told that rather than sold one.

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Anywhere within the M25 — and if you're a little bit outside it, we'll still make the effort to reach you.

Signs of a battery or charging fault

  • Slow, laboured cranking when you turn the key
  • A rapid clicking noise and no crank at all
  • Dashboard lights dim or the car resets when you try to start it
  • The car starts fine after a run but is dead the next morning
  • Stop/start has quietly stopped working
  • Battery or charging warning light on the dash
  • The car has been standing unused for several weeks

What the mechanic typically checks

Before fitting anything, the sensible order is to test:

  • Resting voltage and a load or conductance test on the battery itself
  • Charging voltage at the terminals with the engine running, to check the alternator
  • Starter motor draw and the condition of the main earth and positive leads
  • Terminal corrosion and clamp tightness — a surprisingly frequent culprit
  • Parasitic drain, where something is drawing current with the car locked and asleep

Fitting the right battery

Modern cars aren't a one-size-fits-all swap. Stop/start vehicles need AGM or EFB batteries, and many need the new battery registered or coded to the battery management system so the charging strategy matches. Fitting the wrong type, or not coding it, shortens the life of the new battery. Tell us the make, model and registration when you book so the correct unit is on the van.

Jump starts

A jump start gets you moving, but it doesn't diagnose anything. If the car goes flat again, the underlying fault is still there — which is why the mechanic tests the charging system rather than just getting you running and leaving.

When a workshop or recovery is still the right call

Alternator and starter motor replacement is sometimes possible on site and sometimes not, depending on where the manufacturer buried it — some sit behind the engine or need the subframe dropped. Hard-to-trace parasitic drains can need hours of methodical testing, and hybrid or EV high-voltage systems need specialist qualification and equipment rather than a roadside visit.

We'll either get you back on the road, or our experienced mechanics will give you a solution.

Other things we can come out for

Request a mechanic

Call or WhatsApp us and tell us where you are and what the car is doing — you can share your location straight from your phone. Prefer to type it out? Use the request form on the homepage and we'll come back to you.

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Rolling Mechanics is a trading name of Symatec Ltd. We introduce customers to independent mobile mechanics — see our terms & conditions.

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