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Battery not charging from solar

Warning Do not attempt any electrical or gas work yourself. Always use a qualified, MCS-certified, or Gas Safe registered professional for repairs.

What you’re seeing (symptoms)

Your solar panels are producing 2kW or 3kW of power, but your battery percentage (State of Charge) isn’t increasing, or it’s even decreasing as you use power in the house.

What’s normal vs not normal

Normal:

  • The battery not charging if it is already at 100%.
  • The battery not charging if your household appliances are using ALL the solar power currently being generated.
  • Slow charging in extremely cold weather (to protect the battery cells).

Not normal:

  • Exporting power to the grid while the battery is at 20% and the sun is shining.
  • The battery being “Idle” for days during sunny weather.
  • The battery percentage dropping rapidly with very little load.

Likely causes (ranked)

  1. CT Clamp issues: The sensor that tells the battery how much solar is being produced is installed backwards or has come loose.
  2. Incorrect Mode: The battery is set to “Timed Discharge” or “Force Export” instead of “Self-Consumption.”
  3. Full Battery: The battery was charged from the grid overnight (on a cheap tariff) and has no “room” for solar.
  4. BMS Protection: The Battery Management System has temporarily paused charging due to temperature (too hot or too cold).
  5. Communication Error: The inverter and battery are not talking to each other correctly.

Quick checks you can do safely

  • Check your battery app—what “Mode” is it currently in?
  • Check if you are currently exporting power to the grid (your smart meter or app will show this).
  • Check the battery’s temperature in the app (if available).

When to call an installer

  • If the battery has been at 0% for more than 24 hours (this can damage the cells).
  • If you see “Communication Error” or “BMS Fault” on the display.
  • If power is clearly being exported to the grid instead of going into the battery.

Questions to ask your installer

  • “Is the CT clamp positioned correctly on the main incoming tail?”
  • “Is the ‘Minimum State of Charge’ (SoC) set correctly?”
  • “Does the battery firmware need an update to improve charging logic?”

Related NetZeroNow tools & guides

FAQs

What is a CT Clamp? It’s a small clip-on sensor around your main electricity cable. It tells the battery when you have “spare” solar power to store. If it’s wrong, the battery is “blind.”

Should I charge from the grid? Only if you are on a “Time of Use” tariff (like Octopus Flux or Agile). Otherwise, you should save all the capacity for your free solar power.

Why is it slow in winter? Lithium batteries don’t like being charged when they are near freezing. They may limit the charging speed to prevent internal damage.

Can it charge and discharge at the same time? No, it can only do one or the other (or be idle).

What is ‘Self-Consumption’ mode? This is the standard mode where the battery automatically stores any solar power you aren’t using and gives it back when the sun goes down.

Written by NetZeroNow | Last updated on 2026-03-02