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  • Dr. Tobias Weltner
  • Oct 18, 2024

All-In-One Battery Testers

Cheap Yet Effective All-In-One Testers For Capacity Tests And Measuring Internal Resistance

Surprisingly affordable all-in-one testers offer all the necessary measurements to reliably distinguish counterfeit batteries from genuine ones and provide a general estimate of battery health.

The load resistor on top may get very hot during testing (60-80C). No fan or heat sinks are required, but I chose to add some heat sinks nevertheless to minimize the risk of accidentally burning my fingers.

Overview

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

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. The PCB also features solder pads for attaching cables to an alternate battery holder.

Item Description
Power Supply USB-C (left port) or 18650 battery cell (left holder)
Battery Under Test 18650 battery cell (right holder) or external battery (max. 5V)
Charging Lithium Ion, 1A max.
Discharging 1A max (fixed load resistor)

When using this device to charge a battery (see details below), only LiIon and LiPo batteries are supported. The charging voltage is too high for LiFePo4 batteries.

Buttons And Operation

The unit has three push buttons:

  • Power: When off, press to turn on; when on, press to select a menu item or long-press to turn off.
  • Change Settings: Press to increment the currently selected menu item. No decrement is available, so keep pressing until the settings cycle back to the lowest option.
  • Start/Stop Test: Press to start the selected test. Press again to stop it.

Changing Language

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

  1. Turn off the unit.
  2. Press and hold the Menu button while turning the unit on. Once content appears on the display, you can release all buttons.
  3. Turn the unit off, then turn it back on.

Test Modes

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

  • Automatic Testing (LiIon/LiPo only): In AUTO mode, the unit charges the battery under test until fully charged, then discharges it to determine its capacity, and finally charges it again. At the end of the test, the battery is fully charged.

    To select this mode, press the Power button until the Mode menu is highlighted, then press Menu until AUTO is selected.

  • Discharge Test (all battery types): In DSG mode, the unit immediately begins discharging the battery to determine its capacity. Once discharged, the battery remains discharged, with no charging. Use this mode to test non-LiIon/LiPo batteries (e.g., LiFePo4, NiMH, or others).

    To select this mode, press the Power button until the Mode menu is highlighted, then press Menu until DSG is selected.

  • LiIon Charger (LiIon/LiPo only): In CHG mode, the unit functions as a charger for the battery under test. Only use this mode with LiIon/LiPo batteries.

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

The test modes can be further refined by two additional settings:

  • Loops: In AUTO mode, you can perform up to 10 consecutive loops for better accuracy.

    To set the number of loops, press the Power button until the Loop menu is highlighted, then press Menu for the desired number of loops (1-10).

  • Stop Voltage: In AUTO and DSG, you can set a stop voltage at which you want the discharge to stop. This can be useful if you are testing different battery chemistries, i.e. LiFePo4, or would like to make sure that the battery under test isn’t exposed to deep voltages.

    To set the number of loops, press the Power button until the Stop menu is highlighted, then press Menu to set the desired stop voltage (2.5-3.5V in steps of 0.1V).

Controlled Discharge: Resistive Load

The unit uses a static resistive load that can reach temperatures of 60-80°C under test conditions.

Test Results

Test results are displayed in the lower part of the display and constantly updated while a test is running:

  • mAh: currently discharged capacity in mAh
  • mWh: currently discharged capacity in mWh. This is taking into account the battery voltage and voltage drops as well, so it is a more accurate unit to describe the battery capacity.
  • mR: calculated battery internal resistance in milliOhm. This is an indicator for battery quality and health: lower is better. Normal 18650 cells should show an internal resistance of <80mOhm. High drain 18650 cells (capable of delivering high currents) should be well below 20mOhm.
  • Time: Time in hours, minutes, and seconds that the current test has been running.

Power Supply

The unit cannot take power from the battery under test, or else the test results would be inaccurate.

The default power supply is through the left USB-C connector. With this power supply, all three modes can be used.

For portable use, insert a 18650 cell into the left battery holder. This cell powers the unit in DSG (discharge) mode only. You cannot charge the battery under test.

Automatic Charging

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

LED Status
red battery is charging
blue battery is fully charged

When the battery is nearly fully charged, both LEDs may alternate between red and blue for a short period, as the unit apparently does not account for hysteresis.

Remove the left battery if you do not plan to use the unit for an extended period. The unit draws a small quiescent current and lacks under-voltage protection for the left battery. Leaving the battery in the unit unused for too long may deep-discharge and damage the battery.

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(content created Oct 18, 2024)

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