EBL 18650 Lithium Ion "3000mAh" Battery

The battery can be purchased for less than $2 a piece.   But it is a little skeptical that the capacity is actually 3000mAh.  The weight is about 44g, which seems reasonable, perhaps 3-4g short of other comparable cells.  The EBL battery seems to be Ultrafire repackaged: the labeling is similar down to the misspelling of "Sheef-life".  One "official specification" found on another online review site is

• Genuine Ultrafire 3000mAh 18650
• Real capacity: 2900mAh (-100mAh / + 100mAh)
• Internal PCB protection prevents under-voltage at 2.5V and over-voltage at 4.25V. UNIQUE INTERNAL PCB!
• Diameter 18.6+/-0.2 mm (Note: Diameter may not fit all flashlights)
• Height 66.5+/- 0.2mm
• Weight (Typical) Approx. 46 g
• Nominal Voltage: Average 3.7V
• Cut-off Voltage: 2.5V
• Internal Impedance: less or equal to 180 milli-ohm (with PTC)
• Cycle Performance: 90% of initial capacity at 400 cycles
• Cycle life: > 500 cycles
• Charge: Current = 0.5C mA Voltage = 4.2 V End Current = 0.01 mA
• Discharge: Current = 0.5C mA End Voltage = 3.0V

The first discharge test with constant resistive load of 5 Ohms; the battery drains to 3V in about 3hrs.  Integrating the discharge current shows about 2300mAh.  The voltage falls off quickly at around 3.3V.  Discharging with 35-Ohm resistive load yields about 2400mAh.  The integration of charging current back to full capacity also shows about 2300-2400mAh.  So it only has 80% of the stated capacity.  It is in general agreement with measurement by other people.

18650 Battery Shield V3

"18650 Battery Shield V3" charges a 18650 lithium ion battery and outputs 5V and 3.3V.  It claims 4A on 5V and 1A on 3.3V.  It can be purchased for less than $3.

The charge input voltage is from a micro USB connector, going through a diode, to the 1A linear lithium ion battery charger IC, TC4056A by China Fu Man Electronics Group.  The charging current is about 0.6A (the current programming resistor at Pin 2 is 2000Ω, I = 1V/2000Ω*1200).   Taiwan Fortune Semiconductor's DW01-G battery protection IC and China Hottech Semiconductor's 8205A dual n-channel MOSFETs (drain pins tied) provide over-voltage (4.25V), over-discharge (2.4V) and over-current protection, which is set to about 3A (with Rdson of the two FETs 50 milli-Ohms total).  We can get an estimate of the charge current by measuring GND and the negative battery terminal; the gain is 20A/V.

A step-up regulator FP6298 by Feeling Technology generates 5V.  Given that the battery discharge limit to 3A, the 5V output cannot reach the specified 4A.  The actual measured current limit is about 2.6A and 5V output tops out at about 1.5A.

The 3.3V output is generated by 3 parallel Torex XC6206P linear regulators with input from the battery.  The 3.3V output does not seem stable; it is noticed that there is no output capacitor.  Each regulator has rated maximum output current of 200mA.  The current limit is 450mA before foldback.  The dropout voltage is 500mV at 200mA.  The outputs of the 3 regulators are tied together directly.  If the outputs are not exactly the same, the regulator with the highest output voltage will dominate and causes the other two to shutoff.  So the output current is sourced from only one regulator until it starts current limiting.  Surprisingly, the actual measurements show that the output current can reach 1A.  The dropout from the battery voltage is likely to be limiting factor for the output voltage to be in regulation.

A slide switch switches power to the USB A connector, but it does not turn off the regulators.  The idle current is 0.3mA.

The battery holder is backwards, reversed from the polarity marking as a result of layout footprint error.  The marking on the PCB is correct.