Fabia3iow

You may not have caused damage to the CPU, it doesn't mean damage is definitely done by charging through the negative battery terminal......won't say how I know 😏

With your battery, you should try for a replacement whilst it is in warranty, that is what I would try. The resting voltage immediately after a run is normally between 12.2 and 13.0V in the short time I have had the new battery. With batteries it's all a out the charge retention time. A failing one can charge up ok but loses its charge more and more rapidly. If you are leaving your ignition on there will be some circuits activated and drawing current this whilst a battery is in its dying days could rapidly leave you under voltage. The ability of the battery to crank the engine and supply the necessary Amps is also a factor here. I've seen the battery voltage drop momentarily to 10.8V on both new and old batteries so it's not a direct indicator that a battery is in bad condition it is more its ability to hold a charge and having the internal plates in an unsulphated and un warped condition.

Well, my battery was just outside the 3 year warranty before it started to fail and it went downhill for about 18 months before it finally died, I monitored it with a plug in voltmeter during the last year. The new battery is working well. I don't do many miles at the moment but the charge for the first few miles is 14.9V before reverting back to the normal charging and over run charging that you would expect plus stop/start works fine. The new battery has a five year guarantee so I'm hoping it will last that long. I've never looked at battery warranties. Parts generally aren't covered by wear and tear or misuse but only faults due to the manufacturing process or the item not being fit for purpose. With sealed batteries you don't even have to check the acid levels so all they need is a minimal maintenance charge and with 35k you would have achieved this.

I'm approaching 2 years of ownership of my my 2016 1.2 tsi SE and today had my original battery changed at Halfords for one of their EFB013 65Ah ones. Having watched the demise of my original Moll battery using a voltmeter over the past year and reading the stop/start issues on these forums I thought might add what happened with the voltages in my experience. Prior to replacement the battery would charge at 14.9 to 15.0V with the engine running and/or driving AT ALL TIMES but would drop to just above 12V on turning the ignition off falling to 10.8V the next morning and this is the point at which, unsurprisingly, the car struggled to start. With the new battery the charge, whilst driving with the foot on the accelerator was, 12.4V rising to 14.9V when the foot was taken off the accelerator and back to 12.4V when replaced. This was with all aux systems switched off other than driving lights. With the interior fan set at setting 2 the lower voltage was 13.4V. The response time for the voltages to rise and fall with the accelerator movement was 1 to 2 seconds each and every time. Sound exciting? Well it was for me because I was experiencing the much mentioned charging over-run. On returning home after a short drive the resting voltage was 12.8V and holding....and of course the stop/start function has returned whilst the battery is in it's good and new state of charge. This was all with the charge control lead attached to the negative terminal. Now a word of warning. Euro Car Parts, as an example, offered me a cheap standard non EFB or AGM battery when I typed in my car's registration number. I must admit to being surprised at this and it shows these systems are fallible. It doesn't know my car has stop/start fitted. It's good to see the system working as it should (at the moment) but it shows that the over-run charging happens all the time on short trips and not, as has been suggested, only on long trips. This being the case it seems that the system works ok IF you have a healthy battery. Well it does in my case at the moment and I will keep.an open mind and monitor how it goes. If you are getting a constant charging rate of 14.8-15.0V your battery is on it's way out and taking off the battery charge monitor lead will make no difference. Halfords service was excellent by the way, it's annoying you need all the gizmos to fit a new battery and the extra charge (no pun intended) to fit it. If you offset that against the current £20 annual road tax and the fact that you will be paying a chunk of that battery cost if it were a standard battery you feel a little better about it. Anyway those were my findings 🙂