What it means

EcoFlow Err 100 means the Battery Management System (BMS) detected that one or more individual cells inside the pack reached a voltage above the safe limit (typically 3.65 V for LiFePO4 or 4.25 V for NMC chemistry).
The BMS pauses charging instantly to protect the cells.
The unit stays usable on the output side, but won't accept any more charge until the cells balance back down.

Affected Models

EcoFlow DELTA 2 (LiFePO4)
EcoFlow DELTA Max (NMC)
EcoFlow DELTA Pro (LiFePO4)
EcoFlow RIVER 2 / RIVER 2 Pro (LiFePO4)

Common Causes

Cell imbalance — one cell charges faster than the rest and hits the limit before the pack is full
Charging in very cold conditions (below 0°C for LiFePO4) — voltage climbs sharply at low temperatures
Fast-charge mode used continuously without giving the BMS time to balance cells
Aged pack where one cell has drifted in capacity from the others (common after 500+ cycles)
BMS sensor error reading false high voltage (rare)

How to Fix It

Stop charging.

Unplug the AC cable, the car charger, or the solar cable — whatever was feeding the unit.
The BMS has already paused charging, but removing the source resets the state.
Discharge the pack down a bit.

Run a known load on the AC output (a lamp, laptop, kettle) until the unit's state of charge drops by 5-10%.
This pulls all cells back below the imbalance threshold and gives the BMS room to rebalance on the next charge cycle.
Switch to slow charging.

In the EcoFlow app, set AC Charging Speed to the slowest available (typically 200-400 W).
Slow charging gives the BMS time to actively balance cells as the pack approaches full.
The faster Х-Stream or X-Boost modes don't give the BMS that time, which is why repeated fast charges can build up imbalance.
Let it sit fully charged for 4-6 hours.

Once the pack reaches 100%, leave the AC charger connected.
The BMS uses the trickle phase at full charge to bleed energy off the high cells and bring the pack back into balance.
This is the main way LiFePO4 packs self-rebalance and skipping it causes Err 100 to recur.
Check the ambient temperature.

If you've been charging in a garage in winter (below 5°C), move the unit indoors and let it warm up to room temperature before charging.
Cold lithium cells show false-high voltage readings and trigger Err 100 well before the pack is actually full.

When to Call a Professional

Repeated Err 100 on a unit under 2 years old or under 300 cycles is a warranty case — contact EcoFlow with the serial number and a description of the charging conditions.
Don't attempt to open the pack to access cells; the cells are spot-welded and have safety vents that can rupture if handled wrong.