What happens when a battery is delivered and fitted

A dead car isn't always a dead battery. A few quick checks can save you a visit, and they help us bring the right thing. The AA and the RAC both suggest starting here:

Tell us what you found. If the lights are bright and you hear one click, the battery might not be the problem, and we'll say so.

• Fuel. A faulty gauge or a forgotten fill-up catches people out.
• Dashboard lights. If they're dim, flickering or dead, the battery's the likely cause.
• The key fob. If the doors won't unlock, try the spare fob. The fob's own battery may be flat.
• The steering lock. If the key won't turn, rock the wheel gently while you turn it.
• The sound. The AA links rapid clicking to a flat battery or the alternator, and a single click to the starter, its relay or a poor earth.

You don't have to wait until the car's dead. It's often better not to. Booking ahead means you choose the day and the place, rather than the battery choosing them for you on a cold morning.

It's worth booking if the battery's four or five years old and the car's slow to start, if stop-start has stopped working, or if you've needed a jump recently. The RAC says batteries generally last three to five years, and the AA says around five. Autumn's a good time, before the frosts find the weak ones.

The quote form asks for the basics. Give us your mobile number, the registration, the postcode and a line about what the car's doing. If you can, add a photo of the battery's label and say where the car's parked.

You don't need to know the battery type. That's our job. But if you've already bought a battery, say so, and send a photo of its label too.

We ring you back on the number you gave. That's where the work of matching happens. We look up the battery the car left the factory with, check it against your label photo, and confirm the type. An AGM car gets an AGM. An EFB car gets an EFB, or an AGM if you'd like the upgrade and the car accepts it.

We also check whether the car needs registration. The AA says most modern car makers need a new battery coded to the car, so it's a common part of the job. Then we ask about access, give you the price and agree a time. If the price doesn't suit, there's no obligation.

The fit happens where the car's parked, so make sure that spot's legal and safe. The Highway Code asks drivers to use off-street parking or marked bays where they can, in rule 239. Rule 243 rules out stopping within 10 metres of a junction or across a dropped kerb. In London, rule 244 keeps cars off the pavement altogether.

• Leave room to open the bonnet fully, or the boot if the battery's there.
• Clear the boot floor or a seat if the battery's under it.
• Have the key ready, and the spare if the main fob's unreliable.
• Find any radio code the car asks for after a battery change.
• Make sure someone will be at the car to hand over the key.

The fitter usually rings when they're close, to check exactly where the car is. In a car park or a block of flats, they may ask you to meet them. They park so they don't block your drive or a neighbour's.

First, they look at where the car's parked. If it's somewhere unsafe to work, like a tight bend or a busy junction, they'll ask for it to be moved. Then they open the bonnet or the boot and get started.

Before anything comes off, the old battery gets a proper look. It's how you know the replacement's needed.

The AA says a 12V battery is six cells of about 2.1V each, and if one fails, the battery can't be saved. A battery with a dead cell reads well short of where it should, even after a charge.

1. The case Cracks or a bulge mean replacement, by the RAC's advice.
2. The terminals White or grey crust is corrosion, the RAC explains. Loose clamps cause starting faults that come and go.
3. The voltage On the RAC's scale, 12.6V and above is fully charged at rest, under 12.4V is low, and about 12.0V or less can point to a fault.
4. The tester A handheld tester gives a health reading. Battery University notes these estimate health from internal resistance and can't measure capacity, so the fitter reads it alongside the voltage and the battery's age.

The swap follows the RAC's order. Negative lead off first, then the positive, then the hold-down. On cars with a battery sensor, it comes off with the negative lead. The old battery lifts out upright, and the tray's cleaned.

The new battery goes in the same way round. If there's a vent tube, it's fitted. The hold-down's tightened so the battery can't move. Then the positive lead goes on first and the negative last, with the sensor back in place. Both are tightened, and the covers go back on.

Registration's the next job on cars that need it. The fitter plugs a scan tool into the diagnostic socket and records the new battery, and on some cars its type and capacity. The RAC says many modern cars need registration or an electronics reset after a new battery, and this is that step.

We see it most on Volkswagen Group cars and on plenty of BMW and Mini models, and other makes vary. It's already in the price if your car needs it.

The engine's started and the charging's checked. With the engine running, the RAC looks for somewhere between 13.7 and 14.7V. Some modern cars vary their charging, so the fitter reads it in context, with an eye on the dashboard.

If the charging's not right, a new battery won't stay healthy. The RAC says a battery that passes a test points to the charging system, the starter or the wiring. If we see that, we'll tell you what we found.

For most drivers, nothing feels different afterwards. A few small settings may need resetting. The RAC says some electronic systems take a little while to reset after the battery's been disconnected, so you might need to set the clock, put in a radio code or re-teach the one-touch windows.

On a stop-start car, stop-start may not come back on the first drive. Lots of cars hold it back until the battery's charge is high enough. Drive normally, and it usually returns within a few days.

The old battery goes in the van and on for recycling. A car battery has no place in a household bin, the RAC says. They're well worth recycling: Battery University says about 70% of a lead-acid battery's weight is lead that can be reused.

The battery doesn't have to be fitted at home, since mobile car battery fitting comes to the car. A work car park, a station car park or a friend's drive is fine, as long as the car's parked legally and there's room to work. Some sites need a contractor to sign in, or won't allow work on cars, so check first.

Tell us the full address, the level or bay, and who'll have the key. If you can't be there, a colleague can hand it over and collect it again afterwards.

Most fits go smoothly. These are the things that can slow one down, and most are easy to avoid if we know about them on the callback:

• The car's boxed in, so the bonnet or boot won't open fully.
• The battery's under an electric seat and the seat won't move without power.
• The boot's locked and the battery's inside it. The fitter can usually power the car through the jump posts first.
• The hold-down's missing or broken.
• A lead's badly corroded or damaged and needs repairing.
• A battery you've bought doesn't match the car.
• The fault isn't the battery at all.

A battery fit is for a car that's parked. If you've broken down in a live lane, phone 999 straight away. Rule 277 of the Highway Code says that if you can't get to the left or out of the car safely on a motorway, you stay in it with your seat belt and hazard lights on and call 999 for the police. Once the car's been moved somewhere safe, send the form.