12V Battery Check

Every car has
a 12V.

The 12V battery is the most-ignored failure point in any modern vehicle. In an EV or PHEV, it's the silent culprit behind phantom fault codes, failed wake-ups, and "the car won't start" on your driveway. A proper load test takes 15 minutes. It's £25.

All vehicle types · Mobile · No call-out fee within 10 miles

Book 12V check → WhatsApp to arrange

12V Load Test · £25

Full diagnostic report

Modern vehicles — particularly those with stop-start systems and AGM or EFB batteries — require the new battery to be registered to the car's Battery Management System (BMS) via OBD after fitting. Without registration the vehicle may continue charging the new battery at the wrong rate, shortening its life. PAD offers BMS registration as a standalone service (£35) or as a £20 add-on alongside a load test. Coverage is strong on pre-2021 European vehicles — see the registration section below for full details on what's supported.

Voltage at restMeasured

Cold cranking ampsUnder load

State of charge%

Internal resistancemΩ

ReportPass / Fail / Monitor

On site · ~15 minutes · plain English report

When you need one

Three symptoms.
One root cause.

All three of these problems have a single, often-missed explanation: a 12V battery that's failing under load. Fifteen minutes of testing rules it in or out with certainty.

01 — WON'T START

EV & petrol both

"The car's been sat for a day or two and now it won't wake up. On an EV, that's almost always the 12V, not the main battery. Same on petrol — the big battery doesn't start the engine, the 12V does."

→ Load test confirms

02 — PHANTOM WARNINGS

Dash lights up for no reason

"ABS, airbag, battery, tyre pressure — all lit at once then clear themselves. Modern cars panic when voltage dips below 12V briefly. Replace the 12V and the gremlins disappear."

→ Voltage sag detected

03 — PHEV 12V DEATH

Every 18 months

"BMW 330e, XC60 T8, Golf GTE. The petrol engine barely runs, the alternator barely charges, the 12V slowly dies. It's not a defect — it's a known pattern."

→ Catch it early

What's included · £25

A proper test.
Not a voltmeter reading.

Voltage at Rest

Baseline reading

Battery voltage with the car off. Below 12.4V is flat, below 12.2V is a problem, below 11.8V is past saving. Just a starting point — on its own this doesn't prove much.

Cold Cranking Amps

Under-load measurement

Professional tester puts the battery under real starting load. Rated CCA vs measured CCA tells you if the battery can actually do its job. This is the test that matters.

Internal Resistance

Age & health indicator

As batteries age, internal resistance climbs. Measured in milliohms. A fresh battery reads ~4 mΩ; a tired one reads 8+. Predicts failure months before it happens.

Written Report

Pass · Monitor · Replace

Clear verdict and a printed/emailed report. If the battery's fine, you know. If it's on its way out, you get a realistic timeframe — not a sales pitch.

Already booked an EV or PHEV battery check? 12V load test is included at no extra cost.

Battery registration

New battery fitted?
It needs to be told.

Most modern vehicles can't just accept a new 12V battery and carry on. The engine management system needs to be told a new battery has been fitted — so it adjusts the charging strategy correctly. Skip this step, and the alternator treats it like an old battery, overcharging it and cutting its life short.

BMS Reset · Standalone£35

Battery registration only

You've already fitted a new battery. We come out, connect up, run the BMS reset via professional diagnostic equipment, confirm the vehicle has accepted it, and send a report. Takes around 20 minutes on-site.

Book BMS reset

BMS Reset · Add-on+£20

With your 12V load test

Already booking a 12V battery check? If the result is replacement, we can carry out the BMS registration on the same visit for £20 more. No second appointment, no separate call-out.

Book 12V check

Coverage — what we know

Pre-2021 · European vehicles

BMW, VAG group, Mercedes, Volvo, Ford (EU spec), Vauxhall — BMS registration is well-supported and reliable across this range. Confident coverage.

2021 and newer · all makes

Coverage becomes less predictable. Many European models still work. Non-European vehicles (Toyota, Honda, Hyundai, Kia etc.) vary by model, year, and whether the ECU is locked. We'll tell you honestly if we can't confirm before you book.

Not sure about your vehicle?

WhatsApp us your reg before booking. We'll check coverage and give you a straight answer — we won't take a booking we can't fulfil.

We're actively expanding coverage as tooling improves. If your vehicle isn't currently supported, ask us again — it may well be by the time you need it.

Common questions

12V questions.
Short answers.

You can check resting voltage, yes — but that only tells you if the battery is currently charged, not whether it can deliver power under load. A professional load tester measures cold cranking amps and internal resistance; that's what predicts failure.

The 12V runs all the electronics the main battery doesn't reach — lights, infotainment, wake-up circuits, central locking. It's charged from the HV battery via a DC-DC converter. When the car is off for long periods, the 12V slowly drains. EVs are actually harder on 12V batteries than petrol cars in many cases.

Usually one of two things: parasitic drain from a faulty module (something staying awake after the car sleeps) or wrong battery spec. Modern cars need AGM or EFB batteries with specific ratings — a generic replacement will fail fast. Our test identifies both.

Not directly — PAD focuses on diagnostics, not parts. But the report includes the exact spec you need (AGM/EFB, CCA, case size) so any garage or Halfords can fit the correct one. Or we can recommend a local partner.

About 15 minutes. The test itself is quick; most of the time is getting to the battery and reporting findings clearly. We come to you — no garage visit needed.

Book your 12V check

Fifteen minutes.
Proper testing.
£25.

Mobile across Pontypridd and RCT. Clear report, same day. Works on any vehicle type — EV, PHEV, hybrid, petrol, or diesel.

Book 12V check → WhatsApp first

Professional load tester

Measures cold cranking amps, internal resistance, and state of charge — on site in fifteen minutes.

Every car hasa 12V.

Three symptoms.One root cause.

A proper test.Not a voltmeter reading.