Noticeable quality issues with new JBD BMS (4S & 8S) – incorrect reading on first cell – anyone else seeing this?

[Loeti]

Hi everyone,


I wanted to share a recent experience that honestly surprised me.
Over the past few years, I have installed more than 20 JBD BMS units (4S and 8S) in various projects (boats, camping setups), and I have never had any issues – they have always been reliable.


However, in the last two months I purchased two 4S BMS and one 8S BMS, and all of them have the same problem: the voltage of the first cell (counting from the negative terminal) is being measured incorrectly by the BMS.

• The voltage was checked directly at the connector with a multimeter → correct.
• Replaced the cable harness → no change.
• Connected the new BMS to an existing, perfectly working project → problem persists.

This rules out wiring, connectors, or the battery itself as the source of the problem. To me, this clearly points to an issue within the BMS hardware.


My current conclusion:
At the moment, I would advise against purchasing JBD BMS until it is clear whether this is an isolated case or part of a current quality problem.


Question to the group:
Has anyone else experienced similar issues with newly purchased JBD BMS in recent weeks or months?

 

[mikefitz]

being measured incorrectly by the BMS.

How much incorrectly? I have seen 7mV on one JBD, corrected by recalibration of the BMS.

 

[Loeti]

How much incorrectly? I have seen 7mV on one JBD, corrected by recalibration of the BMS.

More details about my issue:


4S:

• First BMS ordered on June 12, 2025 (120 A)
• Second BMS ordered on July 26, 2025 (100 A)

On both units, the voltage of Cell 1 is displayed about 80 mV too low.
With the first BMS, I experimented with the voltage calibration. The result was slightly better, but the reading now fluctuates significantly – between about –5 mV and +10 mV compared to the actual cell voltage.
Since I have not yet found a way to reset the calibration back to factory settings, I have not attempted this on the second BMS.
The calibration is also not a standard function in the official JBD manufacturer app, and I am currently in contact with the seller’s support team.


8S:

• Ordered on June 23, 2025 (100 A)

For Cell 1, the voltage is displayed about 40 mV too low.
During longer observation, there is also a noticeable drop roughly every 20 seconds, which can result in an error of over 150 mV.

 

[Loeti]

Problem fixed, everything is fine again!

 

[max2k]

Problem fixed, everything is fine again!

how did you fix it?