In short
- Below about 0 to 5 °C the BMS blocks charging to protect the cells.
- One cell reaching its upper limit stops the whole pack, even at 85 or 90 %.
- With closed-loop communication, the battery tells the inverter how much current it accepts; a low limit looks like a fault.
An EG4 battery can refuse charge for several reasons, and they look the same from the inverter screen: zero amps going in. Each reason leaves a different trace in the battery data.
Cold cells
LiFePO4 must not be charged below freezing, and the BMS blocks or reduces charging when the cell temperature is low. Garages and sheds in winter are the usual places. Look at the cell temperature, not the room: a battery takes hours to warm up.
One cell is already full
The pack charge may show 85 or 90 %, but if one cell reaches its upper limit the BMS stops the charge for everyone. The cell spread at that moment gives it away: one cell clearly higher than the rest. Balancing will slowly fix it, faster if the pack spends time near the top.
The inverter is told to stop
With closed-loop communication, the battery sends a maximum charge current and voltage to the inverter. If those values are low, the inverter obeys and the battery charges slowly or not at all. A cable problem can also make the inverter fall back to safe, low values.
Settings and limits
An inverter set to stop charging at a given voltage or charge level, a time-of-use window, or a grid-charge setting switched off can all leave the battery where it is. Compare the inverter settings with what you expect the battery to do.
Reading it from the battery side
EG4 Monitor reads each battery through its RS485 or CAN port and shows the charge, every cell, the temperatures, the current and the alarms, on its screen, on your Wi-Fi and in Home Assistant. When the charge stops, you see at once whether a cell, the temperature or a limit is the reason.
Common questions
My EG4 shows 100 % but the cells are uneven. Is that normal?
A small spread at the top is normal. If one cell keeps reaching the limit well before the others, keep an eye on it over a few weeks.
Does EG4 Monitor replace the closed-loop cable to my inverter?
No. It uses a free communication port and only reads. The link between battery and inverter stays as it is.
Can the box warm the battery or change its limits?
No. It reads values and sends alerts, for example when the temperature drops, but never changes a setting.
