18650 Li-Ion battery test

Generally available Li-Ion 18650 branded and no-name batteries of various capacities were used for testing.

The cells tested come in protected (protected) and unprotected (unprotected) versions.

Pictured below are the batteries tested

Each battery was fully charged with a smart, fully automatic charger Xtar VC2SL before the discharge test

The internal resistance IR (Internal Series Resistance) of the cells was measured using a RC3563 tester

The capacity of the cells was tested using artificial electronic load RIGOL 3021 with a battery test function.

We will carry out a capacity test expressed in mAh (milliampere-hours) by discharging the batteries using an electronic load with a constant current of 1 A to a voltage of 2.8 V.

Discharging Li-Ion batteries below a certain value, i.e. over-discharge, may cause an irreversible chemical reaction and affect the life of the battery. For this reason, cell manufacturers provide a cut-off value for the discharge voltage of the battery ("Discharge Cut-off Voltage"). The values vary, e.g. 2.5V for Panasonic NCR18650A, 2.75V for Samsung ICR18650-26J1. As the no-name batteries do not have detailed technical data, we set the cut-off value for the discharge voltage at 2.8V.

Below are the discharge characteristics of the NCR18650B (3350 mAh) Panasonic battery

For this battery, the discharge cut-off voltage is 2.5V. The discharge characteristics are shown for currents of 2C (6700mA), 1C (3350mA), 0.5C (1675mA) and 0.2C (670mA).
The highest capacity can be obtained by discharging the cell with 1C = 670mA. The horizontal dashed line labelled: "2.8V (End of discharge)" shows the capacity differences for different discharge currents. You can see that the lower the current, the higher the capacity.

Below are the discharge characteristics of a 2600 mAh cell to 2.8V with a current of 1A.

The internal resistance of the battery IR (Internal Series Resistance) determines how quickly the voltage drops when the cell is connected to a load. The higher the resistance, the greater the voltage drop.
The lower the internal resistance, the faster the battery charges. The batteries we tested were brand new and this parameter did not show anomalies.

18650 cells come in protected and unprotected versions. 18650 battery means:
18 mm - diameter
65 mm - length
0 - cylindrical cell

Most branded 18650 protected and unprotected cells have the following protection:

PTC (Pressure, Temperature, Current): protection against overheating caused by a short circuit, or too high a current. Circuit built into most branded 18650 cells.

CID (Current Interrupt Device): pressure valve that will permanently shut down the cell if the cell pressure is too high (this may be caused by over-charging).

These protections do not protect the cells from over-discharging and over-charging.

Protected batteries use:

PCM (Protection Circuit Module): protection against over-discharge (<2.5V), over-discharge (>4.2V), and over-current. There is a circular PCB with electronic components under the negative pole, so protected cells are about 4 to 5 mm longer than unprotected ones. They may not fit standard holders.

The figure below shows the differences:

1 - Unprotected
2 - Protected

Test results:

#	BATTERY SYMBOL	MANUFACTURER	DECLARED CAPACITY	MEASURED CAPACITY	INTERNAL RESISTANCE (IR)	PCM PROTECTION
1	INR 18650-30Q	SAMSUNG	3000 mAh	2872 mAh	18 mΩ	NO
2	INR 18650-29E	SAMSUNG	2850 mAh	2714 mAh	24 mΩ	NO
3	INR 18650-35E	SAMSUNG	3500 mAh	3266 mAh	27 mΩ	NO
4	INR 18650-25R	SAMSUNG	2500 mAh	2395 mAh	17 mΩ	NO
5	US18650VTC5	MURATA/SONY	2600 mAh	2484 mAh	17 mΩ	NO
6	NCR-18650A	PANASONIC	3100 mAh	2910 mAh	38 mΩ	NO
7	B-M18650/3200	MACTRONIC	3200 mAh	2484 mAh	68 mΩ	YES
8	RAC0026	MACTRONIC	3350 mAh	3114 mAh	69 mΩ	YES
9	Li-ion 3400 mAh	MACTRONIC	3400 mAh	2985 mAh	79 mΩ	YES
10	Li-ion 2600 mAh	XTAR	2600 mAh	2460 mAh	76 mΩ	YES
11	Li-ion 3500 mAh	XTAR	3500 mAh	3217 mAh	78 mΩ	YES
12	Li-ion 2200 mAh	XTAR	2200 mAh	2223 mAh	67 mΩ	YES
13	Li-ion 3300 mAh	XTAR	3300 mAh	2795 mAh	69 mΩ	YES
14	ICR 18650CC	EUROPOWER	2150 mAh	2181 mAh	30 mΩ	NO
15	ICR 18650	EUROPOWER	2500 mAh	2554 mAh	38 mΩ	NO
16	ICR 18650CIL	EUROPOWER	2400 mAh	2387 mAh	35 mΩ	NO
17	ARB-L18-2600	FENIX	2600 mAh	2422 mAh	51 mΩ	YES
18	EV 18650-32M	EVERACTIVE	3200 mAh	2868 mAh	42 mΩ	YES
19	Li-ion 4800 mAh	SDNMY	4800 mAh	875 mAh	70 mΩ	NO
20	GH 18650 3.7V Li-ion	HOTFIRE	4800 mAh	1158 mAh	62 mΩ	NO
21	WZS 18650 5800mAh	ANBAO	5800 mAh	185 mAh	100 mΩ	NO
22	GH 18650 3.7V Li-ion	ULTROFITE	6800 mAh	445 mAh	120 mΩ	NO
23	8800 mAh 3.7V	VARLONPAN	8800 mAh	912 mAh	52 mΩ	NO
24	ICR18650-26J	SAMSUNG	2600 mAh	2498 mAh	41 mΩ	NO