My wife's Jag has stop/start, it rarely works, as she simply does not use the car enough to fully charge the battery, the same applies to all our cars, I have three Lidi smart chargers, two are 3.8 amp, one is 5 amp, and both show when charge is completed, however during COVID I was moving the charger car to car, and using an energy meter to show when charged, and it became apparent even when the charger says complete, the battery is often not fully charged, the smaller of the chargers had a very basic system, it would charge to 14.4 volt, then drop charge rate to 0.1 amp, and the voltage would then slowly drop to 12.8 volt at which the charge rate would go to 0.8 amp, until at 14.4 volt again.
This produced a graph, and as time went on, one could see the time between the charger turning up the charge rate was slowly getting longer and longer, until it was reduced to once a day, always at the same time, so I assume the engine management computer sends info to Jaguar at that time every day.
So it seems a battery takes around 10 days to fully charge, how many days is dependent on how long between charges, and age of the battery, before the Kia battery failed, it reached a point where it would not drop from the 0.8 amp charge rate. But with today's absorbed glass mat lead acid batteries, also called valve regulated lead acid, (AGM or VRLA) one needs a so called 'smart' charger. And around once every 6 months, put the battery on charge for an extended time, a day or two, and I know after doing that my wife's Jag stop/start works again, and we use it not working as a sign the battery needs charging again.
