Hello again,
Well there is a basic requirement for charging an Li-ion cell, and that is to limit the current and regulate the voltage. The current is limited based on the size of the cell and the voltage is regulated to under 4.200v. The voltage regulation must be very carefully controlled, while the current limit is a bit more flexible as long as you dont go over the rating for the cell.
As an example, those 18650 cells usually charge at 1 amp with a set voltage limit of 4.15v or so. What this means is that when you first connect the cell it draws 1 amp but its voltage cant get up to 4.15v yet so it ends up being lower like 3.5v or something like that. As time goes on and the cell takes more and more charge, the voltage rises up to 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, and then the voltage regulator starts to take over and limit the voltage so the current starts to drop, 0.9 amp, 0.8, 0.7, 0.6, ..., 0.3, 0.2, and then finally the current drops to 0.1 amps and that would be considered fully charged for a 2 Ahr cell (C/20).
So the basic idea is to limit the current until the voltage gets up near 4.2v and then regulate the voltage. Because of the way voltage regulators work anyway, the voltage regulator will not kick in until the voltage gets close to the set point anyway, so it's basically a current limted voltage regulator circuit. These circuits are quite simple to build and so maybe you are looking at too complex of a circuit to begin with anyway. If you have a wall wart that can put out say 500ma you can build your own much simpler and probably more reliable too.
A little note about safety...
Most problems with Li-ion cells occur during charge, so a cell should never be left alone while charging. These things can actually catch fire so they can cause a lot of problems if something goes wrong with the charging process.