4-Channel 18650 Battery Capacity Tester Review

I recently got my hands on a bunch of old 18650 cells through a friend. After holding them off for two weeks, I decided to build a UPS using these cells. But when I started testing these batteries for their capacity, more than 80% of them turned out to be very bad as they could not hold any charge (only a couple of hundred milli amp hours). I decided it is not worth continuing further. An 18650 Battery Capacity Tester (18650 lithium-ion battery capacity tester) is very useful is situations like this.

I’ve had a very rudimentary tester for years but 3 months ago I bought this fancy looking 4 Channel 18650 Battery Capacity Tester solely because it could test 4 18650 cells simultaneously. The best thing is the module could charge and discharge the cells (which the basic model couldn’t do as it was only a discharger). In this write-up, I would like to review the 4 Channel 18650 Battery Capacity Tester. I have been using this for almost 2 months now and ready to share all my experiences.

Introduction

18650 Lithium Batteries are the main source of energy to power small devices such as flashlights, laptops to high power devices such as cordless power tools and electric vehicles (cars, e-bikes, scooters, etc.). While there has been a significant development in the field of battery chemistry and packaging, the good old 18650 Lithium Battery is still popular due to its relatively low cost and high energy density.

Many DIYers (including myself) use 18650 Lithium Batteries to build battery packs for storing solar energy or powering a wide range of devices.

Sourcing 18650 Lithium Batteries

The simplest way to source lithium batteries is to buy new batteries. But this can be tricky. You must find a local seller who sells genuine lithium batteries (which is easier said than done). Another way to do this is to go online and look for reputable sellers on AliExpress (or Alibaba) or other similar sites. Don’t buy 18650 cells that claim to have a capacity of more than 3,600 mAh.

Salvaging 18650 batteries from old electronics (laptops or power tools) and re-using them in small projects is a good way to give them a new life instead of throwing them away (where they potentially end up in a landfill).

Need for Testing Battery Capacity

If you bought some new 18650 batteries from a very good source and are sure about the quality of those batteries, then you can expect to get close to the rated capacity from those batteries.

What if you are not sure about the quality of the batteries? In case you got salvaged batteries (like I did), then what percentage of their rated cycles was used? What capacity can you expect from them?

There is no simple answer to these questions and the only way to determine the capacity of 18650 Lithium Batteries is to subject them to a series of charge and discharge cycles and calculate the capacity. Instead of manually taking these numbers, you can make use of dedicated lithium battery capacity testers that are designed specifically for 18650 cells.

What’s in the Box?

We have the Battery Capacity Tester unit in an anti-static bag and a pry tool to take the 18650 cells out of the holder. I found this tool to be very useful as it was extremely difficult to eject the batteries normally. There is nothing else in the package (not even a user manual or a quick start guide).

4-Channel 18650 Battery Capacity Tester Hardware Overview

Let me take you through the hardware, layout, and the design aspects of the 4 Channel 18650 Battery Capacity Tester. The first thing I noticed when I took the unit out of the package was it has two PCBs. Interestingly, all the components are present only on the top PCB while the bottom PCB was used only as a support and protection board.

On top, we have four holders to insert 4 18650 batteries. Each slot is named CHN1 through CHN4. Keep an eye on the polarity of the holder. Both the PCB and the holder itself has clear ‘+’ and ‘–’ markings. Above each holder, we have screw terminals for corresponding channels. They have a direct connection to the respective batteries.

In the center, we have a 30x10mm fan. Looks like it is a fixed speed fan without any speed control. There are two USB-C Ports on either side of the fan. The port on the left corresponds to channels 1 and 2 (CHN1 and CHN2) while the one on the right is for channels 3 and 4 (CHN3 and CHN4).

Just below the fan, there is the colorful LCD. I will show the elements on the display later. And below the display, there are four buttons with labels ‘M’, ‘S’, ‘R/S’, and ‘CHN’. Each channel has LED indicators below the respective holders.

If I disassemble the 4 Channel 18650 Battery Capacity Tester, you can see the logic and control circuitry on the backside of the PCB. They scrapped off the name on the main controller IC. The charging IC is the popular TP4056 and we have four of them. So, each channel gets its own lithium-ion battery charger IC. Interestingly, the charging and discharging of the channels are completely independent.

Apart from the main controller and the charge controllers, the PCB has a bunch of miscellaneous ICs such as 74HC595 Shift Register, CD4051, and some Lithium Battery Protection ICs (8205HA).

The unit has four discharge resistors, just below the fan. I think the fan runs at full speed to keep the temperature of these resistors as stable as possible.

User Interface

The “user interface” part of the 4 Channel 18650 Battery Capacity Tester includes the LCD in the middle and the four buttons below it. While my unit came with English language in the UI out-of-the-box, some users are reporting their units have Chinese language. You can easily switch between the languages by pressing and holding the ‘M’ key while you power on the unit.

Display

With that information aside, let us look at the different sections of the display. We can divide the display layout into two vertical halves. The left half shows different parameters of the battery such as:

• Current Voltage
• Charge/discharge Current
• Battery Capacity in mAh
• Energy Rating of the Battery in mWh
• Internal Resistance of the Battery
• Cumulative Running Time

The right half of the display shows:

• Channel Number (1 through 4)
• Current Status (STA)
• Working Mode (MODE)
• Voltage Limit to Stop Discharging (STOP)
• Number of Charge/Discharge Cycles You Want (LOOP)

Buttons

Just below the display, we get four buttons. Here are the functions of each button.

The ‘CHN’ button switches between battery channels 1 through 4. When you select a particular channel, you can see the stats of the battery connected to that channel as well as set different parameters exclusive to that channel.

Let us go to other side and look at the ‘M’ button. This is ‘Menu’ button that selects one of the three items in the Menu section of the display (MODE, STOP, and LOOP). Note that the ‘M’ key doesn’t change the values of the corresponding menu item, it just switches between the menu items.

In order to set the parameters of a particular menu item, we have to use the ‘S’ button, which stands for ‘Switch’.

For instance, if we use the ‘M’ key to highlight the ‘MODE’ option, then we can use the ‘S’ key to set the mode between CHG (Charge), DSG (Discharge), and AUTO (Automatic Mode).

Similarly, you can highlight the ‘STOP’ option using the ‘M’ key and set the lower limit of the discharge voltage using the ‘S’ key. This 4-channel 18650 Lithium Battery Tester supports discharge voltages in the range of 2.5V to 3.5V (both included) with an increment of 0.1V for each click.

When you select the ‘LOOP’ option in the menu using the ‘M’ key, the ‘S’ key allows you to set the number of charge/discharge cycles you want the unit to perform on a particular battery (1 to 9). For the LOOP count to become effective, you have to set the operation mode to ‘AUTO’. All these parameters are channel specific and are independent to other channels.

Once you set all the parameters, you can use the ‘R/S’ button to Run or Stop the operation (corresponding to that channel).

Update: After receiving a new information from the user “NO,” I can confirm that when you press and hold the ‘M’ key for about 3s, all the four channel with start simultaneously. However, the ‘Mode’ will become ‘AUTO.’

Testing 18650 Batteries

As I mentioned earlier, I have a bunch of 18650 cells, all salvaged from old electronics. The pink cells are slightly premium ones with a capacity of 2,600mAh. I know these are some what good quality cells but they are old. The blue cells have a capacity of 2,00mAh and I think they are a lost cause (couldn’t hold charge for long). So, I’ve decided to use two pink and two blue cells and test them in a single go.

Discharge

First, I wanted to discharge all the cells to 2.7V. Using the combination of ‘M’ and ‘S’ keys, I’ve set the mode to DSG and cutoff voltage to 2.7V. Then clicking the ‘R/S’ button started the discharge operation. The STA changed to DSG on the display. I had to repeat this process for all the channels. The indicator LED (below the battery holder) started blinking during the entire discharge process.

After a while, the operation ended (indicated by STA as END and LED is stable) and all the cells discharged to 2.7V (settled around 2.8V after cool-off period also known as rubber band effect).

Charge

For charging, I didn’t have to set any parameters as all I had to do was set the mode to charging. When I hit the R/S button, the STA on the display became CHG and unit started charging the battery. The indicator LED below the battery holder started blinking. Then I proceeded to charge all the other batteries.

After more than two hours, the channels 3 and 4 (with the blue batteries) were fully charged. The STA became END and the indicator LED was fully on. We can stop the operation at any time by pressing the ‘R/S’ button (STA will become STOP and LED will be off).

Sometime later, channels 1 and 2 (with pink batteries) were also fully charged. After repeating these tests (charging and discharging) a couple of times, both the pink batteries came out really good with 2594mAh and 2605mAh capacity. The blue cells, on the other hand, were bad (could only hold 850mAh and 863mAh capacity).

Auto

As I know that the blue cells are of no use, I’ve decided to sacrifice them for testing the ‘AUTO’ mode of the 4-channel 18650 Lithium Battery Capacity Tester Module. I set the mode to ‘AUTO’ and the number of cycles to ‘3’. The unit automatically charged and discharged the cells three times. Interestingly, it did not show the readings such as the battery capacity and energy capacity until the last discharge action started.

After some searching, I found that if we set the loop count to 1 in AUTO mode, then it will not display the capacity while charging but only during charging. If the loop count is more than 1, then the capacity rating will work on during the last discharge operation.

During both manual charging and discharging operations, the unit displays the capacity values. When you change the mode or restart the unit, the capacity readings will be reset.

Performance of 4-Channel 18650 Battery Capacity Tester

First of all, the unit is very intelligent when it comes to power supply and its distribution. The module has two USB-C Ports; the USB-C Port 1 (to the left of the fan) supplies power to channels 1 and 2 while the USB-C Port 2 supplies power to channels 3 and 4.

When I connect only one power supply (either USB-C Port 1 or USB-C Port 2), then we can charge only the corresponding channels. For instance, with power on USB-C Port 1, I can only charge CHN 1 and CHN 2 (similarly with the other power supply).

However, discharging is slightly different. You can discharge any number of channels even with a single power supply as all it had to is provide power to the electronics, display, and the fan.

If you want to charge four batteries, then you have to connect two 5V⎓2A USB power supplies.

Current Draw from Individual USB-C Power Supplies

Next, I connected USB Meters (one is FNIRSI FNB58 and the other is AVHzY CT-3) to both the USB power supplies and measured the output current in different scenarios. Here’s what I observed:

With power in either USB-C Port 1 or USB-C Port 2 and the unit in standby (without any batteries), the current draw was around 25mA. When I connect both power supplies, the current draw from USB-C Port 1 was 1mA while it was 24mA from USB-C Port 2. Even with batteries inserted (unit still in standby i.e., no charging or discharging), the values were almost the same.

Next, I inserted a battery in CHN 1 and connected power to USB-C Port 1. In charging mode, the total current draw was 1.2A. Here, 1A is for charging the battery (as indicated by the display) and the remaining 200mA for powering the board (electronics, display, and fan).

When I connect both power supplies, the charge current (1A) is coming from USB-C Port 1 while the power to the board is coming from USB-C Port 2.

For the next test, I connected battery to CHN 4. Now, the USB-C Port 2 supplies the charge current while the USB-C Port 1 powers the board.

Things are slightly interesting when it comes to discharging though. No matter how many channels you connect for discharging, the overall current draw is around 200mA. However, if you connect both the power supplies, then current from USB-C Port 1 is around 40-50mA while it is 150-165mA from USB-C Port 2.

Accuracy of Readings

To check the accuracy of the voltage and current values displayed on the module’s LCD, I’ve taken one battery out and connected it externally through a multimeter. I am happy to say that both the voltage and current reading are accurate. The only negative thing is the lack of enough resolution for the readings (only two places after the decimal).

Resistance Measurement

Internal resistance of a battery determines its current carrying capability. This particular lithium battery tester uses the DC 2-wire method to measure the internal resistance of the battery. I don’t have a proper battery resistance measuring instrument to verify the accuracy.

That said, to get proper internal resistance readings, place a fully charged battery in any of the holder and select that particular channel. Wai for a few seconds and the display will show the battery voltage and the internal resistance (mR indicates milli Ohms). For 18650 batteries, the value in the range of 20 to 80mΩ is considered excellent, up to 200mΩ is good and anything, over 350 or 400mΩ means a dead battery.

Can You Change Charge/Discharge Current?

No. We cannot set either of the charge and discharge current. The maximum value for both these parameters is 1A. While the charge current is set by the TP4056 circuit (which has a maximum of 1.2A Charge current), the discharge current is dependent on the discharge resistors and the control circuit.

The only thing you can set is the lower limit of the discharge voltage.

Temperature

The batteries stayed relatively cool during the entire operation (multiple charge and discharge cycles). However, during discharge, the large power resistors on the back were burning up (95°C). Here’s an interesting observation. There are four resistors for dissipating power as heat. Each resistor is associated with only a particular channel. Here you can see channels 1 and 2 discharging while channel 3 just finished discharging and 4 is idle for some time.

While charging, the main charge controller IC (4056) become pretty hot (over 75°C). The rest of the components and including the batteries were at normal temperature.

Price

I bought this battery capacity tester from Banggood. The price of the 4 Channel 18650 Battery Capacity Tester at the time of writing this review was around ₹1,700 (around $20) including shipping. Is it worth it? If you frequently work with 18650 Lithium Batteries on small projects and want to test their capacity accurately, then yes, it is a worthy piece of kit.

Conclusion

To conclude this review, I really liked the 4-channel 18650 Lithium Battery Capacity Tester. You can charge, discharge, and measure capacity of four 18650 batteries independently. This is much better than the basic single channel 18650 capacity tester that I have. The only things I didn’t like were the lack of another digit in the resolution of current and voltage and not being able to set the discharge current. Other than this, I think the 4-channel 18650 battery capacity tester is a decent kit to have in your collection.