What it means

EcoFlow E11 means the Battery Management System (BMS) stopped charging because the pack — or an individual cell in it — reached a voltage above the safe limit.
The unit stays usable on the output side; it just won't take any more charge until the cells settle back down.
Usually it's cell imbalance (one cell charging faster than the rest), charging in the cold, or repeated fast-charging that hasn't given the BMS time to balance the pack.

Affected Models

EcoFlow DELTA 2 / DELTA 2 Max / DELTA 3 (LiFePO4)
EcoFlow DELTA Pro (LiFePO4)
EcoFlow DELTA / DELTA Max (NMC chemistry)
EcoFlow RIVER 2 / RIVER 2 Max / RIVER 2 Pro (LiFePO4)

Common Causes

Cell imbalance — one cell hits the upper voltage limit before the pack is actually full
Charging in cold conditions — lithium cell voltage climbs sharply at low temperatures
Continuous fast-charging that never lets the BMS run its balancing phase
An ageing pack (500-plus cycles) where one cell has drifted from the others
A faulty charger or input feeding too high a voltage
A BMS sensor reading false high (rare)

How to Fix It

Stop charging.

Unplug the AC cable, the car charger, or the solar input.
The BMS has already paused charging — removing the source resets the state.
Run the pack down a bit.

Power a load on the AC output until the charge level drops 5-10%.
That brings all cells 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 the AC charge speed to the slowest option.
Slow charging gives the BMS time to balance cells as the pack approaches full; the fast X-Stream modes don't, which is what builds up the imbalance over time.
Let it sit fully charged for a few hours.

Once it reaches 100%, leave the charger connected.
The BMS uses the trickle phase at full charge to bleed energy off the high cells and rebalance the pack.
Skipping this is the main reason E11 keeps coming back on LiFePO4 units.
Check the temperature.

Don't charge a pack that's been out in the cold.
Bring it to room temperature first — cold cells read false-high and trip E11 well before the pack is really full.

When to Call a Professional

A repeated E11 on a unit under two years old or under roughly 300 cycles is a warranty case — contact EcoFlow with the serial number and a note of how you've been charging it.
Don't try to open the pack to get at the cells; they're spot-welded and have safety vents that can rupture if mishandled.