Can this solution do the job of disconnection the charger if not needed and connect it if needed?
It has 'problems'.
All readily available MOSFETS have a reverse polarity "body diode" from drain to source. In the case of a P Channel FET connected as shown, the body diode will conduct when Vdrain is more positive than Vsource. Alas, this is the situation that occurs in your circuit when the charger has power removed.
One solution is to use series connected opposite polarity MOSFETs with the sources connected and the gates connected. This arrangement is often used in LiIon cell protection circuits.
10 uA drain is 8765 hours/year x 10 uA = 88 mAh/year
= ~ 1.7 mAh/week
Okay, lots of stuff to talk about.
The thing about battery charging is that the battery has its own voltage, so resistance is only half of the story. If the charger is at 12 volts, and the battery is at 11.6, then the .4 volts difference is all that is pushing the current into the battery. This small voltage divided by whatever resistance it finds in the cables and battery determines that current. You might see a 100 amp peak, say when starting an actual car. That causes a rather large voltage transient.
And then, that isn't exactly right either. The voltages that you see while charging will be really very close to each other, and what's actually happening is you are replacing electrons in the battery chemistry to make its reaction go backwards. Its just a lot easier to model this mathematically as an ideal voltage source behind some internal resistance.
But the resistance is a real thing. Professional tools actually place a small value of AC current through the cell and take an AC voltage reading across the cell. This and Ohm's law gets you the value of the internal resistance for the pack or cell, wherever you can get terminals to check it. But, generally, this won't matter to you.
Hooking it all up together will work, with the caveat that diode Vladimir mentions needs to be in the line so the battery doesn't discharge through it. It may be built into the alternator already, maybe not. Do check that. What will happen is that when the battery voltage and the alternator voltage are the same, with no other loads connected, no current will flow.
Best Answer
Feasible: yes
Useful: no, because the power needed by a smartphone is orders of magnitude larger than what such a (kinetic) generator generates.
A (non smart) wristwatch needs only very little power, it can run for years on a small button cell. This amount of power can easily be generated by a kinetic generator.
A smartphone has a large battery and needs charging almost daily. Unless you want to violently shake your phone for a couple of hours every day, a kinetic generator will by far not satisfy the power needs of a smartphone.