🧪 EXPERIMENT: Power Bank Efficacy vs Output Current
Intro
Most modern smartphones support fast charging using high current (2A, 3A, 4A+) and/or high voltage (9V/12V+) to increase total charging power.
Small power banks use several cells in parallel, so it's 1S and typical rated voltage is 3.7V while maximum 4.2V.
Energy conversion efficacy depends on output power (voltage and current). Let's test power bank at different current/voltage to understand the difference between total delivered energy and output current.
Aliexpress
 | $7.67 — Color: PD Black 22.5W |
Power Bank
It's cheap power bank case with my 21700 rechargeable batteries.
SW6208S Specs
- Port: AABCL
- VIN: 4.5-13.5V
- VIN: 16V
- Battery Cell: 1S
- Ichg.MAX=5A
- Pout.MAX=22.5W
- VOUT=4.5-12V
- Iout.MAX=5A
- MOS: Internal
- Fsw.MAX=300-600kHz
- I2C: Yes
- Protocols: PD/PPS/QC/AFC/SCP/PE/SFCP
- NTC: Yes
- Display mode: 3-5 LED/1888
- Package: QFN-50_5x5mm
Teardown
The plastic housing has scuffs and scratches (after outdoor use and in the dirt):
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Top cover screwed by 4 screws. It's possible to install up to four 21700 cells::
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Internal PCB:
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Work Progress
Test Results
CC=1A U=5V
| Experiment № | 1 (20260413) | 2 (20260421) | 3 (20250422) |
| Energy | 45.0384 Wh | 43.1319 Wh | 45.1159 Wh |
CC=2A U=5V
| Experiment № | 1 (20260415) | 2 (20260416) | 3 (20260417) |
| Energy | 39.8210 Wh | 39.5352 Wh | 39.3290 Wh |
CC=3A U=5V
| Experiment № | 1 (20260409) | 2 (20260419) | 3 (20260420) |
| Energy | 32.3358 Wh | 33.4163 Wh | 31.3009 Wh |
CC=1.5A U=12V
| Experiment № | 1 (20260423) | 2 (20260424) | 3 (20260424) |
| Energy | 35.0408 Wh | 33.9297 Wh | 32.7107 Wh |
CC=2.5A U=9V
| Experiment № | 1 (20260426) | 2 (20260427) | 3 (20260428) |
| Energy | 32.5848 Wh | 31.8828 Wh | 32.6879 Wh |
Analysis Results
I’ll average each set to make trends clearer:
| Output Power | Average Delivered Energy | Loss vs 5W |
| 5V / 1A (5W) | ~44.43 Wh | baseline |
| 5V / 2A (10W) | ~39.56 Wh | -11% |
| 5V / 2A (10W) | ~39.56 Wh | -27% |
| 12V / 1.5A (18W) | ~33.89 Wh | -24% |
| 9V / 2.5A (22.5W) | ~32.38 Wh | -27% |
Plot
Conclusions
| 🟢 | Experiments confirmed dependency of total delivered energy and output current. Higher current -> less delivered energy. That means is some cases it make sense to disable fast charging to increase conversion efficacy and as a result delivered energy. |
| 🟡 | For 2S/4S+ power banks results might be different. |