Pylontech US2000 showing SOC drift after cold snap — anyone else seeing this?

Noticed my US2000 has been reading about 12% higher than actual since we had that frost last week. Sitting in my static caravan setup with a Victron MultiPlus-II and the DVCC all configured correctly, so it's not a settings issue as far as I can tell.

Temps dropped to around -4°C overnight and the battery shed isn't insulated. Pylontech's BMS seems to have lost its reference point — did a full charge to 100% and it still hasn't recalibrated properly. SOC showing 87% but the Cerbo GX voltage suggests it's closer to 75%.

Has anyone done a manual SOC reset via the BMS button or is that a bad idea mid-cycle? Seen a few threads on Victron Community about similar drift but nothing specific to cold weather causing it.

@Pylontech_Wizard this is a known issue with the US2000 — the internal BMS recalibrates SOC via coulomb counting, and cold temperatures reduce actual capacity whilst the BMS hasn't yet performed a full charge cycle to resync itself.

The fix is straightforward: force a full absorption charge (58.4V for a 48V pack) and hold it until current drops to roughly 0.05C. That gives the BMS a proper "top" reference point to recalibrate from.

Worth checking your Victron DVCC settings too — specifically that SVS (Shared Voltage Sense) is enabled and your charge current limits aren't cutting absorption short before the BMS has time to sync.

In my experience after a prolonged cold snap, one good full charge cycle usually pulls the SOC reading back within 2-3% accuracy. If it persists after two or three cycles, the pack may warrant a closer look at cell balance.

Just to add to what @BarryWood is saying — cold temperatures genuinely hammer lithium iron phosphate chemistry in terms of voltage response, so the BMS can lose its reference points. What's worked for me is doing a deliberate full charge cycle right to absorption, letting it sit at 100% for a good 20-30 minutes so the BMS can resync. Make sure your Victron charge voltage is set correctly for Pylontech (53.2V for the US2000) and that DVCC is actually taking the BMS limits rather than overriding them. After one proper full cycle mine usually corrects itself within a day or two. Also worth checking your caravan's ambient temp around the battery — if it's still dropping below about 5°C overnight the drift can keep recurring until things warm up properly.

Really common issue this time of year with static setups — the thermal mass of a caravan means the batteries can sit at genuinely low temps overnight without you realising. Worth checking the actual cell temperature readout via the Pylontech console or through VRM if you've got that set up.

One thing nobody's mentioned yet: if your batteries dropped below around 5°C, the US2000 may have restricted charge current automatically, which throws the coulomb counting right out. A full charge cycle to absorption once temperatures recover usually helps the BMS resync properly. Set your Victron to do a proper bulk-to-absorption run and give it time to settle — don't cut it short. The SOC figure should gradually correct itself over a couple of cycles rather than jumping back instantly.

How cold did it actually get inside the storage space? 🌡️

Really good thread, this — @Pylontech_Wizard, one thing worth trying that hasn't been mentioned yet: force a full charge cycle up to the absorption voltage and hold it there until the tail current drops right off. The US2000's BMS will use that as a proper reference point to resync the coulomb counter. I did exactly this after our cold spell in January and the drift corrected itself within a couple of cycles.

Also worth checking your Victron CCGX or Cerbo logs to see whether the battery actually hit 100% SOC during those cold nights — my guess is it didn't quite get there, which compounds the drift over time. The VRM portal is handy for spotting this pattern across a few days.