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Bluetooth Battery: How To Calibrate SOC% and Actual Capacity Readings

To connect to the SOK bluetooth battery, search for ABC-BMS on google or apple store and install on your phone.  When you open the app, it will automatically connect to whichever battery it finds first.  If you have multiple batteries, you can choose which one to connect to by clicking on the top menu and then selecting the battery that has a serial number correlating to the sticker on the top of the battery.

You will notice the SOC and capacity reading, but they are initially incorrect.  In order to make them correct, you have to do 2 discharge/charge cycles.

Steps to Calibrate the BMS:

  1. Check the voltage on the terminal, it should be 10V~14V.
  2. Before connecting anything to the BMS, access the Bluetooth app.  Click on the menu in the top right, select “search device” and click on the appropriate battery by matching the serial number printed on the top of the battery.
  3. After ensuring nothing is connected to the battery, click on the menu again and access the “Basic Settings” menu.  Then, click “Idle Calibration” and press OK.
  4. Discharge the battery using a 12v DC load connected to the terminals directly.  Let it run until it stops on its own.  After the battery is fully discharged, the BMS should be cut off, the Voltage on the terminals should be 0V.  An inverter is likely unsuitable as they often have too high of a low-battery shutoff to trigger the BMS to shut down.
  5. Wake up the battery: connect a lifepo4 battery charger on the terminals and turn it on.  It should be wake up and the charger should start pushing current into the battery, BUT not all lifepo4 battery chargers can wake up the battery.  If you need further help waking up the battery, please check this article:  How to Wake Up A Sleeping Battery
  6. After you wake up the battery, keep the lifepo4 battery charger running until “C MOS” indicator on the home page of the app turns off.
  7. Repeat the step 2, still using a DC 12v load discharge until the battery turns off.
  8. Repeat the step 3, wake up the battery.
  9. Charge the Battery , check the app, the SOC and capacity should be correct.  If the capacity is more than 5% different than what the battery is rated for (for example over 105ah on a 100ah battery) then repeat this process again.

Using an inverter:

If you are using an inverter to drain the battery, it is very likely that the inverter has a low-voltage shutdown that is at a higher voltage than the battery.  If you are using an inverter for most of the discharge, then you must switch to a DC load at the end to finish draining the battery until the BMS shuts off.  It is essential that the BMS shut off for this process to work.

Are the calibration cycles required?

Not necessarily.  They are only important if you plan to use the Bluetooth app for SOC% monitoring.  If you have a separate monitor such as a SmartShunt or BMV-712, then you can skip this process and just use the shunt.  The battery operates completely independently from the SOC% readings.

What causes the SOC% to become inaccurate over time?

The app does not determine SOC based on voltage like a lead-acid battery monitor. The BMS uses shunt resistors and it counts the coulombs to determine SOC, just like an external shunt.

The reason why the SOC in the app becomes inaccurate is it doesn’t use a set point of reference for the capacity.  Instead, it updates the capacity every single time the battery is recharged. Small inaccuracies over time build up and this affects the calculated capacity, which in turn affects the SOC. The greater majority of external shunts use a constant value for capacity and reset SOC% to 100% when they detect full charge.

When should the calibration cycle be repeated?

If the app reports a capacity outside of the following range, repeat this calibration process, starting with step 4:

  • 100ah Battery: 95~110ah
  • 206ah Battery: 200~220ah


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