This is a small and inexpensive solution to charge most 4.2V Lithium-Ion cells.  It uses a true CC/CV algorithm and can work with pretty much any 5V USB-C power source.  The default peak charge current is approximately 1A, but it can be adjusted lower by changing out the current sense resistor (see table below for approximate values).  

This version also has some battery protection onboard, to protect against overcharge/undercharge and overcurrent conditions.

The default resistor value is 1.2K Ohms, which provides approximately 1A peak charge.  For a nominal fee, we will reflow a different resistor onto the board, which you can choose by selecting your required resistor from the dropdown menu.

You can read HKJ's excellent review of this charging IC here.

You will need to solder some leads on to make this work with your desired setup.
There is no polarity protection on the battery side!  If you hook it up to the battery backwards, it will fry the IC.

Specifications:

• Input Voltage: 4.5V-5.5V (USB-C)
• Charge Precision: 1.5%
• Full Charge Voltage: 4.2V 
• Dimensions: 25mmx19mmx10mm
• No Reverse Polarity Protection
• Red and Green Status LEDs

Resistance vs. Output Table

Here is some charging data from HKJ's review: