Ford kuga 12v battery issues

Just replace the battery. It's most likely an 8 year old battery at this stage and it's struggling to hold a charge or start the car.

You need a proper battery tester as measuring the voltage doesn't tell you anything unfortunately.

I'd agree the consensus to replace the battery

Ford use smart charging so the voltage will range from 12v-16v depending on the load and battery state

accume its the 2.0 tdci as you didnt state which engine ?

You can let the battery connected IMO, just ensure the negative charger cable is attached to a (the) earthing stud on the car body and NOT to the battery negative terminal, the car BMS system will then see that and use it in its calculations for the required charge, not sure about Ford's charging methods but my battery is never charged beyond 85% SOC, presumably to make room for the allways charging voltage of 14.8 ish volts on overrun, it will be interesting to see how long my original battery lasts because in 63 years of VWs, all lasted for ever, apart from one, and were only replaced precautionery after 10/12 years as the cars were being passed down the line, all charged at a constant 14.2/14.4V, the one that required replacing, after 5/6 years, was on my first car, a 6V, 1963 beetle.,

I often wonder what "kills" a battery apart from a failed cell, wonder does the internal battery resistance increase to a level that the voltage drop while trying to crank the engine not leave enough voltage bearing in mind that the solenoid which probable only takes ~ 60A to slowly rotate the starter pinion while pulling it in and closing the main contacts to apply full starter voltage. I think (but could be mistaken) that I measured the cranking current on a (Petrol) Formel E Golf at 300A on a cold winters morning, most cars will start well within say 3 secs, so the battery only requires to provide, 300*3/3600, 0.25AH, the sqroot of nothing of battery capacity, even if the starting current was doubled then still only 0.5AH required.

The internal resistance of my 59AH battery was 6.6mOhms after 18 months and just recently, after almost 7 years has "only" increased to 7.4mOhms, so a 300A crank will drop the voltage by 300*7.4/1000, 2.22V voltage drop but of course, say with a 600A crank (diesel??) will drop the voltage by 4.5V which doesn't leave a lot of actual cranking voltage. Don't know what a new battery internal resistance is but possibly around 1.0/2.0 mOhms??.

For interst, my battery (after 18 months) had a SOC of 85% and a "Usable battery charge" of 38AH, latest reading shows SOC of 79% and a usable battery charge of 27AH. (59AH EFB battery).

Another thing that puzzles me is that my older non smart alternators charged at a constant 14.2/14.4V yet the battery only required topping up by a few thimbfulls of distilled water once a year or so, so when does overcharging start, rememer all the commercial travellers that drove for hours on end up and down the country without any overcharging problems.