Hello everyone,

I have a 2017 Ford S-Max, and have had a couple of battery issues with it. It may just have been bad luck, but the original battery appeared to fail three years after I bought the car, and the replacement battery had issues within 12 months. After being burned the first time with a flat battery, I bought a Bluetooth battery monitor, and I have left it fitted since. 

I have been using the monitor to keep an eye on battery levels and charging levels. Often when I'm driving the car I see full charge being applied to the battery from the alternator , however I do also note that charging can also be sporadic. I've attached a few graphs from the Battery Monitor to demonstrate what I mean, but I can see charge levels fluctuate quite rapidly whilst driving. I can't see any correlation between the charge level and engine RPM or equipment being used in the cabin. My reason for looking at this more closely, is that when I do use the Battery Monitor from home just to keep an eye on the battery levels I do see the battery level fluctuate - sometimes the levels can look quite healthy, other times, it can look dangerously low (below 12v)

I appreciate cars have had intelligent charging built-in for them for sometime, so this may just be a simple case of the car only applying charge when it needs to. However, as you can see from the graphs, this intelligent charge does not appear to be particularly intelligent; the charge levels can fluctuate wildly within a few seconds, and I'd imagine it causing more damage than good to a battery. Obviously one of my biggest fears is to  lose  another battery, especially with the wife and kids in the car!

I've checked the connections on the Battery Monitor to ensure that it's not a simple case of a mis-reading. It's entirely possible the monitor isn't of the highest quality (bought from a large online global retailer, for a reasonably low price!) However, it's quite tricky to attach a multimeter and take readings whilst drive the car!

Do these charging graphs look representative of what you would expect to see? Or could this indicate perhaps there is some issue with charging the battery, either the alternator or something that's trying to be more intelligent? If it does indicate an issue, does anyone have any ideas of anything I should be looking to check?  I know if I take this to a garage, it'll be behave on that day and be an absolutely fine charging voltage of around 14.7V. I do see that happen too, and this battery is 12 months old and hasn't failed yet, so it's not a terminal/clear issue  

If anybody has any ideas or previous experience or observations, then I am very interested to hear them.
 

Thanks very much in advance

Pete

 

Those graphs and charging rates look perfectly normal 👍. Remember that while you are driving the car is using equipment all the time. For example, Electric Power Steering, ABS brake module, Air conditioning compressor. As equipment switches on and off the load on the battery and alternator is constantly changing. The smart charge will adjust the alternator voltage (within set parameters) to optimise  the battery charging and to reduce emissions caused by unnecessary loading of the alternator.

The factory set charging default is most probably set to 80% meaning that the car will not charge the battery beyond a State Of Charge (SOC) of 80% no matter how far you drive and at what speed. Some vehicles for example like the Focus Mk4 can have the SOC adjusted to a higher level like 95% using FORScan, which many owners (myself included) have done. Regrettably we live in an age where reducing emissions is a case of 'Smoke and Mirrors' (pun not actually intended) so by restricting the alternators ability to fully charge the battery does mean for many motorists that there is the need to top up the charge every 5 or 6 weeks using a smart battery charger.

   

Thanks so much for this info, and reassurance! I had just assumed that the charge rate would be more binary - i.e. if it's charging, then it's putting out at 14v or so. And if it's not needing to be charged, then the monitor is reporting the battery's voltage. So, it's good to know that it will vary the voltage, and that's what I'm seeing.

Also, thanks for that graph too - I read that batteries should be charged to 12.5/12.6V to be healthy, but I agree, I often see lower levels, probably due to, quite frankly, slily charging logic - it certainly feels like it's hosed a couple of batteries on my side. Arguably, I may have been too hasty to replace the initial battery - but I'll put that down to experience. I'll not be too worried if I see the voltage lower from time to time.

I'll keep an eye on this and see how it goes!

Thanks again for your help and info.

Pete