Home batteries

Battery stuck at certain percentage

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 battery reaches a specific percentage (e.g. 99% or 10%) and “hangs” there for several hours, even with plenty of solar power or high house demand. It may also refuse to charge past a certain limit (e.g. 80%) regardless of the weather.

What’s normal vs not normal

Normal:

  • Balancing: The battery sitting at 99% for an hour while it finishes “cell balancing” at the top of the charge.
  • Target SoC: The battery stopping at 80% because you have set a specific “Charge Limit” in the app to extend battery life.
  • Safety Buffer: The battery stopping at 10% because that is the manufacturer’s recommended minimum safety floor.

Not normal:

  • The battery being stuck at 0% for several days.
  • The battery dropping from 20% to 10% instantly (suggests a dead cell).
  • The battery being stuck at 50% for 24 hours while solar power is being exported to the grid.

Likely causes (ranked)

  1. Imbalanced cells: One cell in the stack has reached the voltage limit before the others, causing the BMS to stop the whole pack to prevent damage.
  2. Calibration drift: The BMS has “lost its place” and needs a full 0% to 100% cycle to re-learn where the top and bottom of the capacity are.
  3. App settings: A “Max SoC” or “Min SoC” limit has been set in the inverter’s advanced menu.
  4. Temperature lockout: The battery is too cold (below 5°C) and the BMS has restricted the charge/discharge to protect the chemistry.
  5. Firmware mismatch: The inverter and the battery are running incompatible software versions, leading to communication errors about the State of Charge.

Quick checks you can do safely

  • Check the app limits: Look for “Reserve,” “Min SoC,” or “Max SoC” settings. Ensure they are set to your desired usable range (e.g. 10% to 100%).
  • Check the temperature: Is the battery in a cold location? Lithium batteries often refuse to charge if they are near freezing.
  • The ‘Full Cycle’ fix: If you have a cheap night tariff, force-charge the battery to 100% from the grid. This often “forces” the cells to balance and resets the calibration.
  • Check the lights: Look at the physical LEDs on the battery modules. Are any showing a “Fault” or “ALM” (Alarm) red light?

When to call an installer

  • If the battery remains stuck at a specific percentage for more than 48 hours.
  • If you see a red “Alarm” light on any of the battery modules.
  • If the system works but the percentage “jumps” erratically (e.g. 100% to 70% in 10 minutes).

Questions to ask your installer

  • “Can you remotely trigger a ‘Deep Calibration’ or ‘Cell Balance’ cycle?”
  • “Is there a firmware update available for the BMS or the Inverter?”
  • “Does the cell-level data show any individual cells with a significantly lower voltage than the rest of the pack?”

Related NetZeroNow tools & guides

FAQs

What is SoC? State of Charge (SoC) is the percentage of energy currently in your battery compared to its total capacity. It’s essentially your “fuel gauge.” Why 99%? Charging from 0% to 90% is fast. The last 1-2% is much slower because the BMS has to carefully trickle-charge the cells to ensure they are all exactly the same voltage. This is called “balancing.” Will 0% damage it? A “reported” 0% is fine, as there is always a hidden safety reserve. However, leaving it at 0% for weeks can lead to “deep discharge,” which can permanently kill the battery. Can I reset the BMS? Usually, you can’t “reboot” just the BMS. You have to shut down the whole system (AC and DC) for a few minutes. How often should it reach 100%? Ideally, at least once a week. This gives the BMS a chance to “re-calibrate” the 100% marker and balance the cells.\n

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