How to change your Car Battery – Fitting & Coding

Is your car not cranking over, or maybe taking its sweet time to? Maybe your headlights turn off when you start it, or you’ve got a ‘low battery’ warning on your dashboard. All of these symptoms, and plenty more, mean you need to change your car’s battery. Luckily, it’s not too difficult, and I’m here to help. So, lets take a look at how you know you need to change it, how to save a boatload of money when getting a new one, how to physically replace it, and if you’ve got a newer car like my 2013 Audi S4, how to tell the car’s computer you’ve replaced it too.

Lets start with how you know you need to replace it. The symptoms I mentioned already are pretty common, even things like your dashboard turning off when you go to start the car all indicate a dead battery. But, that could mean your battery is just out of charge, and could mean your alternator is failing instead. So, there are a few checks you can do. With the engine running, if you can, use a multimeter to measure the voltage. If it’s at 14-15V, your alternator is working and charging the battery fine. If it’s at 12V – or lower – it’s possible your alternator is shot. It’s important to note though, on newer cars like this, and my friends F10 5 Series I’ve done a few videos on already, the battery charging is controlled by a control module, and if it knows the battery is dead it can refuse to charge it.

So, that’s where the second inexpensive tool comes in, the battery tester. This lets you check the health of your battery, either in the car or out. Run a test to have it show you the state of charge and estimated health. In my case it reports that it’s just incredibly low charge, but I know that it’s not quite as healthy as it seems. It’s generally a good idea to replace your battery sooner than later if you have doubts as it’s liable to leave you stranded if it fails while driving.

So that’s why you need to replace it, what about how? Well, you’ll need to find it. In a lot of cars its in the engine bay, but in bigger and newer cars it can often be found under the boot floor. In my case it’s under the spare tyre. So, move everything that’s in the way, then undo any mounts, in my case it’s 5 13mm bolts to remove the spare wheel bracket, and the battery hold down tab. Then you can loosen the 10mm nuts on the battery terminals, removing the negative clamp first. Yank the old battery out, drop the new one in, connecting positive first, then negative, tighten the clamps, then the hold downs and that’s it. Put everything back where it was and you are set.

In older cars, that’s all you need to do. But, especially on these newer German cars, there is a control module for the battery you need to update. In Audi’s case, you’ll need a coding tool. VCDS is a really useful tool to have if you are working on your own car, and lets you code in new batteries too. Ross-Tech, the makers of VCDS have a full video on how to code batteries with the different types, in my case I’ve only got the CAN gateway, CAN protocol type so that’s what I’ll walk you through.

Fire up VCDS, go to the module list and pick 19, CAN Gateway. From the dropdown list pick the battery option, then it’ll show you a value made up of 3 parts, the part number, manufacturer code, and serial number. If you bought a genuine, or direct replacement battery, you’ll have a “BEM Code” sticker with all the info you need on it, for example a VARTA battery should come with that sticker. But if, like me, you bought a non-direct replacement it’s a bit more complicated. If you are replacing your battery with the exact same specs, especially capacity, you can ‘cheat’ and just change the serial number saved by one and press ‘Test’ the ‘Save’ and you are all set. If you are changing the capacity though, which I am from 92Ah to 95Ah you’ll need to find the approved battery equivalent model number and a valid serial code for it.

So, once that’s done you are finally all set. Go for a drive to verify everything is working, check the voltage while the car is running again to make sure the alternator is charging as it should.