I charge from under the hood.
Here is the rational behind it...
IBS monitors the charge to the battery over the life of the battery. As batteries get older they require a higher charge voltage to maintain a constant current (due to sulfate buildup). Chargers use varying currents for different charges. A float is a lower current and a recon or sulfate breaking charge is higher. The concept is to break sulfates off the plates and keep them in solution where they are most effective and makes for a larger surface area on the plates for electrochemical reactions (the way a battery works).
So let's say you always charge directly to the battery, the charge voltage goes up over time and IBS doesn't know this. IBS directly controls the charge from the alternator and will regulate a lower voltage hence lower current because it has not monitored previous chargings. IBS follows a predefined battery life cycle which includes time, temperature and current if it is complete.
At some point in time, IBS will be providing lower current to the battery than the car load. Eventually you will have a dead battery unless you charge it between uses.
I have not found any technical information on this, only block diagrams. However I do know battery and charger theories quit well.
2010 E63 Black sapphire metallic
“Speed has never killed anyone. Suddenly becoming stationary, that's what gets you.”