Lynx Smart BMS 500 NG (A3E4) – Incorrect battery temperature below 0°C (327°C / 1637.5°C)

Q&A and troubleshooting
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1

Hello,

I am experiencing an issue with my Lynx Smart BMS 500 (revision A3E4), serial number HQ2433FGMX9 , related to incorrect temperature readings when the batteries are below 0°C.
The Lynx pilot uses two batteries 300A NG in parallel.

When the ambient and battery temperatures drop below freezing, the Lynx Smart BMS reports completely unrealistic values:

  • 327°C shown in VRM and in VictronConnect (when connected to the Lynx)

  • Later 164°C during temperature rise

  • And most importantly:
    In VictronConnect (Bluetooth) on Battery 1, the internal temperature was shown as 1637.5°C at the same moment.

All other temperature sensors in my system report correct values:

  • Three Victron temperature sensors connected to the Cerbo GX: around –1.5°C

  • MultiPlus battery temperature sensor: around –4°C

As soon as the battery temperature rises above 0°C, the Lynx Smart BMS temperature becomes normal again (0–1°C).
This strongly suggests a firmware or telemetry issue when handling negative temperatures.

All firmwares are fully up to date:

  • Cerbo GX v3.67

  • Lynx Smart BMS v1.15

  • MultiPlus II v556

The issue appears only below 0°C, affects both the Lynx Smart BMS and at least one Smart Lithium battery (via Bluetooth), and disappears above freezing.
This points to a temperature handling bug or a fault in the battery’s internal temperature measurement, which is then propagated to the Lynx.

I will check Battery 2 as well if the issue reappears during the next cold period.

Could the Victron team please review this behaviour?
It seems reproducible and may indicate a firmware issue with negative temperature values.

Thank you.

Jacques

2

During a new cold period, I checked the detailed properties of both Smart Lithium batteries via Bluetooth (VictronConnect → Lynx → Battery).
Batteries reported an internal temperature of 1637°C and 1636.9°C when the Lynx Smart BMS was showing 326°C in VRM.

This confirms that the incorrect temperature does not come from a single faulty battery or a hardware defect, but from a system‑wide telemetry or firmware issue affecting negative temperature values.
As soon as the batteries warmed above 0°C, both temperatures returned to normal.

3

I have a Lynx NG BMS but the temps have only fallen to 2.5°C, I will keep an eye out for this. I have raised the issue with Victron.

4

I have been told it is a display error only and that the BMS functionality is not affected. A firmware update will correct this.

6

Ok. Thank for the feedback.

7

I seem to have the same issue. Adding some additional information.

Product Info:

  • Lynx Smart BMS NG 500 A3E4 (v1.14)
  • Battery NG 300ah PEHQ (v1.01)
  • Cerbo GX mk2 (v3.67)

Error Info:

  • Battery Temperature: 1638.1 C
  • VRM Temperature: 163 C (326 F) (Assuming a digit rounding issue)
  • Ambient Temperature: -5.5 C (22 F)

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