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  • Dr. Tobias Weltner
  • Oct 28, 2024

Single-Battery Tester

Simple Yet Efficient Single-Battery Tester For 18650 Cells, 5V Power Banks, And Other Battery Cell Below 5V

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.

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:

  1. Turn off the unit.
  2. Press and hold the Menu button while turning the unit on. Release all buttons once the display content appears.
  3. 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:

  1. 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.
  2. 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.
  3. 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.

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.

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.

Conclusion

This very affordable tester is a great pick: it reliably tests individual battery cells and is optimized for 18650, but not limited to this battery type. You can also test USB-C power banks provided the power bank is not supplying more than 5V.

Problematic Power Supply Battery

On the downside, this test device can only test one battery at a time because its left battery bay is exclusively reserved for supplying power to the test circuitry. If you need to test batteries only occasionally, this is perfectly fine. However, if you test batteries regularly and in greater quantity, get a beefed up version of this device that has four or even more test bays that all can run simultaneously.

The left battery bay can serve as an internal power supply, making this device portable (which appears convenient at first). However, running this device from an internal battery turns out to be a severe design flaw that can damage your battery:

  • Unreliable: the device is lacking a battery gauge for its left battery (so you never know its state of charge).
  • Damaging: worse, the device has no under-voltage protection for this battery: 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 permanently damage it.
  • Limited Use: while the internal battery in the left bay allows for battery discharge tests without the need for an external USB power supply, when running on battery power the test device is severely limited: it can no longer charge the battery under test, removing much of its brilliance. Accurate battery capacity tests require the ability to first fully charge the battery under test, or better yet, discharge it first to a defined safe voltage level, and then log the charge current until it is fully charged. Neither of this is possible when running on the internal battery.
  • Waste of Space: because of all of the above, the left battery bay is wasting space without adding significant benefit, and this device would be better without it.

Always remove the battery from the left bay if you do not intend to use the device for some time. Better yet, skip this internal battery supply nonsense altogether, ignore the left battery bay and never insert a battery into it. Use an external USB-C power source only.

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(content created Oct 18, 2024 - last updated Oct 28, 2024)

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