Inside a common eBay lithium cell charger - with schematic

Unlike the very shady 120/230V units, this one is pretty good. Nicely made and logical circuitry that has an element of hackability to it for fine tuning to your requirements.

The current setting resistor could be changed to tweak the charge current, noting that higher current will potentially result in thermal self regulation of the charge chip. Use of higher current will also make the charger less suitable for smaller cells. Conversely, you could lower the current to 200mA for softer charging of any size of cell.
The LED resistor could be changed to something in the region of 470 ohm to make the LEDs more visible.

Unlike some other charger which fire springs in random directions and require Rubik's-cube grade reassembly skills, this one is easy to take apart and reassemble.

Here's a generic eBay search link:-
https://www.ebay.com/sch/i.html?_from=R40&_nkw=14500+usb+charger&_sacat=0&_sop=15
Target cost around $4 shipped.

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