Based on measurements on six Liitokala Lii-100 bought in december 2015 I found that the charge voltage for 3.7V LiIon was a little high, all close to 4.25V. I like the uniform result (a quality sign). The voltages are nothing to be alarmed over, but personally I prefer to trade maximum power from a battery for a longer lifespan of the battery so I would like to lower the voltages a little.
I did some reverse engineering on a unit and found that it was easy to change the charge voltage. Two resistors (R5,R6 =150 kOhm, 1%) form a voltage divider for feedback of the output voltage. The fix is so simple that a picture is not necessary. All selectable voltages will be changed by the same percentage (in this example 1.2%).
1. Unscrew the six screws and flip out the circuit board (secure the slider rail with a piece of tape).
2. R5 is found on the topside of the board just besides the +battery terminal (look at post #10).
3. Solder a 6.2 MOhm resistor across R5. Preferably SMD as there are not much space in the height. Can be mounted flat besides R5 and soldered at the ends (I used a 3MOhm plus a 3.3MOhm in V-form between the ends of R5. Resistors can be bought here.
4. Now, the charge voltage is dropped 0.05V.
I will not go into the formula for calculating the parallel resistor, just mention that another 6.2 MOhm (total 3.1 MOhm) across will lower the voltage a further 0.05V and so on. The 6.2 MOhm does not have to be exact. 20% off means 0.01V on output. If you just want to lower the voltage 0.025V then a 12 MOhm resistor will do it.
The charge voltage can be made higher if the operation is done on R6 instead.
Edit: SETTING LOWER CHARGE CURRENTS:
Modding the charger for use with smaller cells is equally easy. High and low current will always be 2 to 1 though.
R10 is sitting just behind the micro USB plug (look at post #10). It is a power resistor of value 0.050 Ohm. This gives 0,5 and 1 A charge current. The charge current is inverse proportional to that resistor (the other big resistor, R19 is for the power bank output). Fortunately there is good space to mount a leaded resistor.
Change R10 into:
0.100 Ohm and get 0.25A and 0.50A (for 14500, 16340, 18350 and larger)
0.200 Ohm and get 0.125A and 0.25A (for 10440 and larger)
0.500 Ohm and get 0.05A and 0.1A (for 10180 and larger)
I just bought two more chargers to make into dedicated ones.
Added: Read about high charge voltage - a safety matter!
and about Lifespan vs. charge voltage.