Homemade portable cell phone charger

A boost IC, an inductor, a capacitor, and a Schottky diode. A total of 4 components.

If you use 18650 lithium-ion batteries instead, 2 18650s (up to 5000mAh) cost about 30 yuan, and the board is only 7 yuan. Adding a protection circuit costs 2 yuan, and it's 40 yuan. Using
one 18650, although the capacity is a little lower, only 2400mAh, the cost is only 25 yuan.

Production process:
A. Buy a 3V to 5V booster board online,
B. Weld it onto a lithium battery ,
C. The lithium batteries used are removed from mobile phone batteries, 10 in total, each 650mAh, connected in parallel to 6500mAh,
D. Put it into a simple plastic shell and fix it

The cover on the board is not ready yet, it is quite simple.

I decorated it and finished it at night. I wonder if it looks good?
A piece of transparent plastic is used on it, so you can see the LED when it is working.

A simple test was done below: charging a Nokia phone through a CA-100C charging cable
. The charging current reached 400mA, which is slightly smaller than expected.
The no-load voltage is 5.60V. In fact, with this board, you don’t need a charging cable, you can charge it directly with a USB to 2mm DC cable.
The measured efficiency: 90%, very satisfactory
. The voltage ripple is also so-so. After all, there is a small chip capacitor at the output end. Don’t expect it to be very good.
Transient waveform, there is no big voltage fluctuation at the moment of current switching.

Conservatively estimated, after this 6500mAh power bank is fully charged, it can be fully charged 4 times with a 58 1320mAh battery. No worries about long-distance travel.

I connected so many batteries in parallel because this battery pack was made 5 years ago and I don't want to waste it. I also have 3000mAh single batteries on hand, and after connecting 4 in parallel, I can achieve more than 10Ah.