Single-Battery Tester - DONE.LAND

This is an affordable all-in-one tester that can identify counterfeit batteries and determine overall battery health and quality. It can test only one battery at a time.

The two load resistors on top (8 Ohms each, connected in parallel) can reach high temperatures during testing (up to 80°C). Adding a heat sink is recommended to avoid accidental burns.

You can easily enhance this device, i.e. by removing the soldered battery holders and adding external test cables, and/or by adding a 3D-printed housing (STL files below).

Feature	Description
Channels	1
Battery Under Test	- 5V max - 18650 battery bay (right side) - USB-C (right side) - Solder pads (next to right battery bay)
Power Supply	- USB-C or - Left battery bay
Discharge Test	- 4 Ohms 10W load resistor - Max discharge current 1A - Units: total mAh or total mWh - Stop-voltage configurable (2.5–3.5V) - No heat sink or fan
Charging	- LiIon and LiPo only - Max charging current 1A
Auto-Test	Yes, charge-discharge-charge cycle with total discharge energy reported
Off-Button	Yes, long-press left push button
Language	English and Chinese, configurable
Firmware	- Version 4.2 - User cannot upgrade firmware
LED	- Red: power-supply battery charging (left battery bay) - Blue: power-supply battery fully charged (left battery bay)
Display	- Color-TFT - Backlight

Overview

This tester can be powered via USB-C (using the left USB-C connector) or by a 18650 cell in the left battery bay.

When powering the device through the left USB-C connector, the left battery bay can remain empty, as it does not participate in testing. If a 18650 cell is inserted into the left battery bay, it acts as an internal power supply, making the device portable. In portable mode, the battery under test cannot be charged. When the device is connected to USB power while a 18650 cell is present in the left battery bay, the cell will be kept charged: a red LED indicates charging, and a blue LED indicates the battery is fully charged.

The battery under test can be a 18650 cell (in the right battery holder) or any other battery connected through the right USB-C connector or solder pads located at the right battery bay. The battery under test must not exceed 5V.

Buttons and Operation

The unit is operated via three push buttons:

Power: Press to turn on when off, select a menu item when on, or long-press to turn off.
Change Settings: Press to increment the currently selected menu item. There’s no decrement option, so continue pressing until the settings cycle back to the beginning.
Start/Stop Test: Press to start the selected test. Press again to stop it.

Changing Language

The unit supports English and Chinese. To switch between languages, follow these steps:

Turn off the unit.
Press and hold the Menu button while turning the unit on. Release all buttons once the display content appears.
Turn the unit off, then on again to confirm the new language setting.

Test Modes and Settings

The unit offers three test modes: AUTO, CHG, and DSG:

Automatic Testing (LiIon/LiPo only): In AUTO mode, the unit sequentially charges, discharges, and then charges the battery again to provide a full capacity assessment. The battery is left fully charged at the end.

To select AUTO mode, press the Power button until the Mode menu is highlighted, then press Menu until AUTO appears.
Discharge Test (all battery types): In DSG mode, the unit starts discharging and logs the discharged energy. It then leaves the battery discharged, so this mode is suitable for non-LiIon/LiPo batteries like LiFePO4 or NiMH that cannot be safely charged with this device.

To select DSG mode, press the Power button until the Mode menu is highlighted, then press Menu until DSG appears.
Charge Test (LiIon/LiPo only): In CHG mode, the unit serves as a charger specifically for LiIon/LiPo batteries, and logs the charge process.

To select CHG mode, press the Power button until the Mode menu is highlighted, then press Menu until CHG appears.

Additional test settings can be adjusted for further customization:

Loops: In AUTO mode, set up to 10 consecutive loops for enhanced accuracy.

To set loops, press the Power button until the Loop menu is highlighted, then press Menu to cycle through the number of loops (1–10).
Stop Voltage: In AUTO and DSG modes, a stop voltage can be defined for discharge tests, ideal for different battery chemistries (e.g., LiFePO4) or to prevent deep discharge.

To set stop voltage, press the Power button until the Stop menu is highlighted, then press Menu to adjust the stop voltage (2.5–3.5V in 0.1V increments).

Controlled Discharge: Resistive Load

The device uses a fixed resistive load that can reach 60–80°C during tests. The load produces a maximum discharge current of 1A.

Performing Battery Capacity Test

You can reliably measure the total battery capacity by either discharging a fully charged battery or charging a fully discharged one:

Charge Test: This approach is efficient if you use the battery until it’s “empty” by your standards, then perform a CHG test. The tester logs the charging energy transferred back into the battery as it recharges.
Discharge Test: For higher precision, use the AUTO test. Here, the tester first fully charges the battery to a specified level, then fully discharges it to a safe stop voltage. In this test, the device logs the total energy drawn from the battery.

The discharge test using AUTO mode starts the battery from a defined level, producing consistent results. However, this test takes longer as it includes three phases—charging, discharging, and charging again—and slightly increases battery wear.

The charging test in CHG mode is faster and reduces battery wear: since the battery would need recharging anyway, the tester simply functions as a smart charger, logging the energy input. The drawback is that there’s no set start level, making the “empty” state subject to user interpretation.

For a more efficient manual testing setup, first run a DSG mode test to discharge the battery to a specified stop voltage, then follow up with a CHG cycle. This way, the battery charges from a defined “empty” state without unnecessary wear. However, the built-in AUTO mode runs the opposite sequence, consuming an extra charge cycle.

1. Select Test Parameters

Before testing, follow these steps to select the test mode and its parameters:

Stop Voltage: Set a safe stop voltage for your battery. 3.0V is generally safe for LiIon/LiPo batteries.
1. Turn the device on with a short press of the left button.
2. Short-press the left button until the STOP setting is highlighted in blue.
3. Short-press the middle button until the display shows the desired stop voltage.
Test Mode: Select the test mode: DSG, CHG, or AUTO.
1. Short-press the left button until the MODE setting is highlighted in blue.
2. Short-press the middle button until the desired test mode is displayed.
Loops: Set the LOOP option. Generally, set this to 1 for a single loop test.

All settings are permanently stored and will stay active until manually updated.

If the display dims due to power-save mode, pressing any button will wake the display to full brightness. Additional button presses will function normally after wake-up.

2. Connect Battery Under Test

Once you have set the test paramaters, connect the battery you want to test. Make sure that the battery voltage does not exceed 5V, especially when testing power banks.

When inserting a 18650 cell into the battery bay, be extremely careful not to reverse polarity, or else you may destroy the device. The polarity is printed into the battery bay: the positive pole is facing you when looking from the side with the push buttons.

Here are your choices:

18650: Insert an 18650 cell in the right battery bay, or
Power Bank: Connect a USB-C cable to the right connector for testing a power bank (not exceeding 5V), or
Alternate Battery Bay: Attach wires to the two solder pads next to the right battery bay for a different battery type.

3. Start the Test

Press the right button to start the test. The display’s STA field shows the test status.

The test stops automatically upon completion. Pressing the right button again will pause or abort an ongoing test.

When switching batteries, turn off the device by long-pressing the left button or disconnecting power. Failing to do so may result in cumulative capacity logging, where the new battery adds to the previous battery’s data.

Test Results

Test results are shown in the lower portion of the display and are continually updated throughout the test:

mAh: Capacity in mAh.
mWh: Capacity in mWh, accounting for battery voltage and voltage drops for an accurate energy measure.
mR: Calculated internal resistance of the battery in milliOhms. Lower values indicate better quality; for 18650 cells, typical values should be below 80mOhm, and for high-drain cells, they should be well below 20mOhm.
Time: The elapsed time for the current test, displayed in hours, minutes, and seconds.

Test results are constantly updated while a test is in progress. In the modes DSG and AUTO, the discharge capacity is measured. In the mode CHG, the charge capacity is measured.

Power Supply

The unit cannot draw power from the battery under test, as this would lead to inaccurate test results.

The primary power source is the left USB-C connector. When connected through this port, the unit can operate in all three modes.

Left Battery Holder / Portable Use

For portable use, insert a 18650 cell into the left battery holder. This will power the unit in DSG (discharge) mode only; it will not be able to charge the battery under test in this mode.

The left battery holder is of such limited use that you may want to as well desolder it. If you keep it, then never leave a 18650 battery in this bay permanently, or else the quiescent current and missing undervoltage protection may destroy the battery over time.

Automatic Charging

When a 18650 cell is placed in the left battery holder, the unit automatically charges the cell once connected to USB power. Two charger LEDs indicate the charging status:

LED	Status
red	battery is charging
blue	battery is fully charged

As the battery nears full charge, both LEDs may alternate between red and blue briefly, as the unit doesn’t account for hysteresis.

Remove the left battery if the unit will be unused for an extended period. The unit draws a small quiescent current and lacks under-voltage protection for the left battery, which may lead to deep discharge and potential battery damage.

Customizations

Unless you want to exclusively test 18650 round cells, at the minimum you should solder a pair of test wires to the test bed and add a convenient connector to it.

I have 3D-printed a round-cell holder that lets me easily insert a wide range of lithium-based round cells.

Housing

The PCB isn’t very practical by default: the left battery holder can only be used to power the tester during discharge tests. For full tests, you need an external USB power supply anyway.

Plus, the left battery bay has no undervoltage protection, and if you indeed use it to power the device, chances are you are damaging or destroying the battery over time.

That’s why I recommend removing both battery bays:

This way, you can place the PCB in a very small housing. Add a pair of test cables to externally connect a battery bay or other means of battery holder.

The built-in TFT display can now be read easily, and you can attach a heat sink to the load resistors.

Here are the STL files for the housing I used:

The heat sink part can be snapped around the two built-in load resistors. On top, there is space for a default 70x21mm heat sink. Since the heat sink can be exposed to temperatures of 60-80C, use a heat-resistant 3D printing material for this part, i.e. ABS.

Conclusion

If you can get this tester for less than €4.00, it may be a nice pick for occasional battery testing: it comes with all test functionality required for a single LiIon cell, and with a bit of customization - housing, removing internal battery holders, adding external battery holder, and possibly a smaller load resistor for a higher discharge current - you end up with a useful battery tester for small money.

Single Cell Testing Only

However, if LiIon battery testing is your thing and you need to regularly test batteries, then this tester isn’t right for you: since it can test only a single cell, and since the discharge current is limited to 1A, it takes considerable time for a test to be conducted.

Plus, it has some design flaws:

Useless Left Battery Bay

The left battery bay is almost completely useless as it is reserved for internal energy supply during discharge tests. Regular testing requires an external USB power supply anyway.

No Gauge: no battery gauge for the left battery (so you never know its state of charge).
No Undervoltage Protection: if you leave the battery in the device for prolonged times, and if you do not regularly connect the device to USB power to recharge it, the quiescent current will eventually deep-discharge this battery and destroy it.
No Use: when powered by the the left battery, the battery under test cannot be charged from it. Only simple discharge tests with previously fully charged batteries can be run off the left battery. This makes no sense.

Lii-M4S: Better Choices

The Liitokala Lii-M4S (not to be confused with the Lii-M4) would be a much better choice for regular LiIon battery testing: you can get it often for less than €14.00, and it comes with four universal bays big enough even for 21700 and 26650 cells.

This single device with its ready-to-use housing, four robust battery slider bays, touch buttons and reliable firmware costs less than four of the hobbyist-level test devices described in this article, and performs much better:

conducts tests on each of its four bays individually
reports both the total discharge and charge capacity.
can also be used as a regular charger, or to bring battery voltage toa safe-for-longtime-storage 3.70V (by automatically charging or discharging the battery as appropriate)
comes with internal load resistors, discharge current can be set to 300mA and 500mA .

Dedicated Dischargers

Another route you may want to take is to stick to cheap and affordable multi-bay LiIon chargers and just add a DIY battery discharger.

Commercial Multi-Bay Chargers With Total Load Current…

For a perfect test environment, invest in chargers that can show the total charging current (like the Liitokala Lii-S8):

Check the charger features carefully before you buy: the 8-bay Lii-S8 for example comes with sophisticated charge current testing per bay, whereas the almost identically-looking 12-bay Lii-S12 is lacking all of these features and works like a simple charger only.

This way, whenever you charge batteries, you get a good capacity estimate for free (and without extensive test overhead).

Whenever you want to really test the total battery capacity, you just need a device that can discharge the battery to a desired level, i.e. 2.8V (for total capacity) or 3.7V (for long-term storage).

…and a Universal Battery Discharger

Below is a very affordable breakout board called HW-586 that can safely discharge any battery (15V max) using up to 3A discharge current.

This module is often available for less than €1.00 and comes with two 5W 8Ohm load resistors. Typically, both resistors are connected in parallel (4 Ohm) resulting in around 1A discharge current.

A more flexible approach is to use just one of the two 5W 8Ohm resistors, and add a 25-50W 2 Ohm resistor.

8 Ohm: permanently connect a 8 Ohm resistor which enables a moderate discharge current of around 500mA.
2 Ohm: add a 2 Ohm resistor in parallel with a 3A switch in series, so you can add this additional resistor only when needed.

By default, the discharger would now discharge with moderate 500mA. If you need a higher discharge current, you can add the second resistor in parallel, dropping total resistance to 1.6Ohm, delivering 2.6A discharge current at 4.2V.

Fixing “Error 3”

Coincidentally, such a setup would also help with the dreaded Error 3 issue:

During the initial seconds of discharging, the module looks for significant voltage drops to make sure the battery under test is actually able to safely deliver the discharge current.

Unfortunately, this alarm is often triggered by the resistance of your battery holder and its wiring, not the battery, once you start using higher discharge currents.

To get rid of it, either use a higher-quality battery holder with less resistance, or use the dual-resistor approach outlined above, and start discharging with the 8 Ohms resistor at 500mA only.

Once the system has stabilized, add the second resistor for the full 3A discharge current.

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