Battery/ alternator issue.

[seanrjordan]

Hi I’ve had an issue with my mk3 Leon this week that has Broke my trust in the car.
on Tuesday I drove around 250miles home from a trip away. All was fine no lights on the dashboard or anything. I then unloaded my car and nipped to the supermarket 12 miles total probably all was well.

I got up the next morning to go to work and my car won’t start and I get the message on the mfd 12v battery low. i take an alternate mode of transport to work. When I return home I jump start the car. I check the voltages with a multimeter and it reads 14.5 volts suggesting to me the alternator is ok. Checked against a neighbours car while that was running and theirs read 14.2v. I’ve checked my cctv and it appears no lights were left on to drain the battery. i didnt have time to mess around charging so have put a new battery in and the car has been fine since.

What puzzles me is that my old battery was purchased in march 2024. is it possible the battery could have died already?

 

[RUM4MO]

A battery dying in just over a year, not typical, but what brand was that new battery bought in March 2024, also what is your typical annual mileage as many battery suppliers will reject warranty claims if the average annual mileage is less than maybe 3,000 miles.

 

[seanrjordan]

A battery dying in just over a year, not typical, but what brand was that new battery bought in March 2024, also what is your typical annual mileage as many battery suppliers will reject warranty claims if the average annual mileage is less than maybe 3,000 miles.

Was a Bosch. Annual mileage is around 7,500 a year.

 

[Walone]

Assuming you

Was a Bosch. Annual mileage is around 7,500 a year.

Assuming your car has stop/start, was the March 2024 battery AGM or EFB? For diesel cars it's usually AGM, and it needs to be coded in to the charging system so that it charges at it's best.

 

[Craig.]

Check the car for any fault codes such as no communication with generator. This will show any issues that may be existing that could cause incorrect charging etc. Best to rule out everything else before blaming the battery.

With that being said, batteries can be faulty. The trash brands like Lion arrive DOA more often than the better brands like Varta, Exide and Bosch.

Check for the manufacturing week and year marker on the battery, see how old it really is. You may have been sold a battery that is already yonks old.

 

[RUM4MO]

Was a Bosch. Annual mileage is around 7,500 a year.

So, that is good and that type of usage should not have caused this.

Next, maybe buy one of these cheap 12 plug in DVMs from ebay, I bought one of them many years ago and it has ended up being plugged into whichever of our cars I'm using - just plugs into the "12V Power" socket, having that lets you "see" what is going on wrt charging, and possibly let you find out what could be causing your problem.

On the subject of battery branding, I too have always dismissed "Lion" as a brand, but then I discovered that most of these "other" battery brands are using batteries from what is meant to be a "well respected" worldwide battery manufacturer - though I'll probably stick with giving brands like "Lion" a miss.

Varta used to build Bosch batteries, maybe still do just using different case plastic colours, JCB (Johnson Controls Batteries and not JC Bamford!) are said to be the biggest proper battery manufacturer, and most Varta batteries fitted to VW Group cars at factory are "Varta made by JCB" which is why you find both names on the original battery if it is a Varta, aftermarket Varta tend to be labelled "Varta DE" ie Varta Germany.

Exide is a brand that I've always avoided when buying a new battery in the past - just based on personal preference, but VW Group use/fit them at factory, my wife's 2015 VW Polo 1.2TSI has an Exide EFB and it has lasted well enough, current mileage 54,000 miles, my older daughter's 2019 Leon Cupra has an Exide EFB and as that car is mainly used in town and Stop/Start is always left "on", it is still alive and working okay at 24,000 miles, but when tested it has dropped down in capacity more proportionally than the Exide in the Polo.

We are Costco members and Costco sell Bosch batteries so on a cost only basis, it makes sense to buy from there as and when required.

Edit:- while it is true that a cheap ebay made in China 12V DVM might not be very accurate, but from my experience, it is close enough for this purpose and gives repeatable results - also be aware that if you switch on the ignition, open the bonnet, then after waiting for "things to settle down", using a quality ie Fluke etc multimeter, measure the voltage across the car's battery then again at the 12V Power Output, you will get different results, so don't worry about that, it is trends that you should be looking for. On the overrun with a battery that has "spare" capacity or otherwise requires charging, the indicated voltage can be up to almost 15V, at idle after driving for maybe 5 or 10 miles, the voltage can again be heading for 15V if the battery needs recharging or is dying, or as low as 12.7V if the battery is healthy and at its normal which is roughly 80% charge - maybe even lower than that quoted "12.7V" - that was just a guess based on what I think that I've seen at warmed up idle.

 

[LeylandVCDS]

Assuming your car has stop/start, was the March 2024 battery AGM or EFB? For diesel cars it's usually AGM, and it needs to be coded in to the charging system so that it charges at it's best.

Usually but not always - my 2.0TDI (2019 stop start) had an EFB fitted from factory, as confirmed by the PR code. I was having constant issues with the (less than 12 months old Bosch EFB battery needing charging every few days, signified by the stop-start not available because of high power usage.
After changing it to an Bosch AGM, and coding it in as such, I haven't had one single issue since - so totally agree that the diesel NEEDS an AGM battery, not an EFB.

I've also got a permanently hard wired digital voltmeter fitted in the coin tray by the driver's knee, and I've noticed that when the EFB battery was in, it was always charging at 14+ volts, now on an AGM battery, it charges anywhere between 11.5 and 14.5 volts, and as such, with the alternator not working at full capacity all the time, it's noticably more fuel efficient too. Standing battery voltage is now al;ways around 12 - 12.5 volts.