Cube Nuride Bosch PowerTube 750 Temperature too high error

[Oleophobic]

This is a repost from my other thread, just to check if the bot can help:

I have a Cube Nuride (Bosch Performance Line CX Gen4 and Bosch PowerTube 750Wh) that’s throwing errors whenever the motor uses more than 180-190W (by my estimation) and shuts down the whole system (orange LED blinking), reporting error 680008.
However, the battery only has 94 cycles and the battery is cool (I literally take the bike out of the basement in which it has been sitting in for 50+ hours at 20°, start riding, and the error is thrown in less than 10 seconds if I pedal hard).
I’ve tried resetting the battery (holding the button on it for a while), I’ve tried unplugging and plugging all the connectors, I’ve even cleared the diagnostic codes using my friend’s Bosch diag, but to no avail.

The bike is out of warranty, and I’m not financially able to replace the battery.
I’m skilled in electronics and repairs so I’m happy to open up things, resolder components, rebuild cables/connectors or even reball chips if needed.
The main issue is that I have no idea where to start, and I hate Bosch for being so locked down and unfriendly to repairs. I’m aware that almost every hardware issue is handled by replacing the whole thing by Bosch, but this isn’t a route I’m willing to go with.

 

[Greg Watts]

This is a repost from my other thread, just to check if the bot can help: I have a Cube Nuride (Bosch Performance Line CX Gen4 and Bosch PowerTube 750Wh) that’s throwing errors whenever the motor uses more than 180-190W (by my estimation) and shuts down the whole system (orange LED blinking), report...

@Oleophobic - error 680008 on a Bosch Smart System is a battery protection trip, specifically a thermal or current-limit fault. The fact that it triggers within 10 seconds on a cold battery at low cycle count is the important clue here: it's almost certainly not the battery cells themselves (those would need to be warm and stressed to genuinely overheat), but rather a faulty NTC thermistor or BMS sensor inside the battery reporting a false temperature.

The Bosch BMS trusts its own sensor completely. If one NTC is reading 60°C when the actual temperature is 20°C, it'll shut down immediately and confidently. It doesn't care what you feel with your hand.

Where I'd start if I were poking around inside: • NTC thermistors - there are typically several embedded in the cell pack. A failed or drifted one will false-trigger thermal protection. These are standard NTC bead thermistors and can be tested with a multimeter (resistance at room temp should be predictable from the part's B-value curve). A shorted one will read near-zero resistance = very high temperature to the BMS.

• BMS connector/ribbon - the interface between the cell sensing harness and the BMS board is a common point of failure. Corrosion or a hairline fracture in a flex cable can cause a single cell group or sensor to read wildly.

• The BMS board itself - less likely at 94 cycles, but not impossible. A failed comparator or ADC channel will misread sensor data.

What makes this tricky: Bosch's BMS firmware is signed and the pack is fully proprietary, so you can't reflash or recalibrate the sensor mapping. You can only fix the hardware the firmware is reading. The good news is that NTC thermistors are cheap generic parts; the bad news is finding which one is drifted without a reference schematic.

Practical next step: If you can open the pack (some Bosch PowerTubes use T20 Torx under the label - worth checking), read each NTC with a multimeter at room temp. At 20°C a typical 10kΩ NTC should read roughly 12 - 13kΩ. Anything wildly off is your culprit.

Worth documenting as you go - there's very little public teardown data on the 750Wh PowerTube specifically, and this forum would benefit from it.