A home battery can still import electricity from the grid while it has charge because the house needs more power than the system can deliver, a reserve or schedule is holding energy back, or protective controls are limiting discharge. Sometimes the monitoring app is simply showing an older snapshot.
A charged battery and a grid-import arrow don’t, on their own, prove something is wrong. The useful question is whether that import is brief and expected, or sustained when the battery should be supplying the house.
Start with the time and the amount
Note when the import happens, how long it lasts and what was running. A momentary reading when a large appliance starts is a different problem from buying several kilowatt-hours through an otherwise quiet evening.
Check the app’s last-updated time before comparing it with your smart-meter display. FOX’s explanation of cloud data and apparent import anomalies describes how a snapshot can catch the inverter responding to a change in demand. The displayed flow can then remain on screen after the actual flow has changed. Update intervals depend on the monitoring system and software; don’t assume every display is live.
Look at the day’s import history as well as the animated arrows. Where your supplier provides interval data, compare matching periods. Keep grid imports separate from total household consumption, which can also include direct solar use and battery output.
The battery has energy, but not enough power
Capacity in kWh tells you how much energy is stored. Power in kW tells you how quickly the system can deliver it. Both the battery and inverter can impose limits. A high charge percentage doesn’t remove those limits.
E.ON Next’s guide to battery specifications distinguishes continuous output from capacity and explains why the grid supplies the balance when demand exceeds the system’s output.
Here’s a hypothetical example during normal grid-connected operation:
- The house is using 6.5kW.
- Solar is supplying 1kW to the home.
- The battery system is delivering its available maximum of 4kW to the home.
- The remaining 1.5kW comes from the grid.
If those flows stay constant for 20 minutes, the import is 1.5 × 20 ÷ 60 = 0.5kWh. These are illustrative figures measured on the home’s AC side; conversion losses mean the energy taken from the battery cells is greater than the energy delivered to the home.
Before buying extra storage, establish whether the limitation is energy capacity or output power. Our guide to adding more batteries to an existing system explains why an expansion doesn’t automatically increase inverter output.
Some charge may be reserved
The percentage displayed in the app isn’t necessarily all available for everyday use. Minimum state-of-charge settings and, where supported, a separate backup reserve can stop normal discharge before the display reaches zero.
For example, Tesla’s Backup Reserve guidance explains that part of a Powerwall’s stored energy can be held for an outage, leaving the remainder for everyday operating modes. Other manufacturers use different controls and terminology.
Ask which reserve applies to your system and why it was chosen. Don’t lower it below the manufacturer’s permitted limits simply to make an import arrow disappear. If the installation has backup capability, reducing its reserve also reduces the energy kept for an outage.
A reserve setting alone does not provide backup power. Our explanation of solar panels and battery backup during a power cut covers the equipment and electrical arrangements involved.
A charging schedule may be doing exactly what it was told
Check the operating mode and the schedule active at the time. A system deliberately charging from the grid is expected to import. Some operating strategies also preserve stored energy for a later, more expensive period instead of discharging immediately.
Record the start and end times, the system clock and any reserve set within the schedule. Include any electricity-supplier or third-party control service: your usual app may not be the only place issuing instructions.
Menu layouts can change. In its guidance published on 17 February 2026, FOX explains the move to Mode Scheduler in Fox Cloud version 2.2.0 and later, and notes that some systems need compatible firmware. Use the guidance for your exact equipment rather than copying an older screenshot.
Save your current settings before asking for changes. For a wider review of reserves, tariffs and control responsibilities, see our battery storage optimisation guide.
Temperature protection can restrict discharge
Cold conditions can change the power available even when the battery still shows charge. The battery management system may reduce output or temporarily hold energy back to protect the cells.
FOX’s guidance for non-heated batteries in low temperatures describes reduced charge and discharge rates and a protective reserve mode for the equipment covered. Its thresholds should not be treated as universal settings for every FOX model or another manufacturer’s battery.
Record the reported battery temperature and any warning message. Ask the installer whether the behaviour fits that model’s protection settings. Don’t improvise heating, wrap the equipment or override protective limits.
When should your installer investigate?
Request a review if substantial imports continue while household demand is modest, charge is above the relevant reserve, no charging schedule explains it and there are no expected temperature restrictions. Repeated alarms or behaviour that changed suddenly also deserve attention.
The installer can check the configuration, firmware, battery communications and the metering arrangement. Where the system uses a current-transformer sensor, its position, direction and coverage need to match the installation. Leave electrical enclosures, sensors and wiring to a qualified installer.
Send a useful record rather than just one screenshot:
- The inverter and battery model numbers, installation date and module count.
- A timestamped screenshot showing solar, house, battery and grid power together.
- The charge percentage, active mode, schedule and reserve settings.
- Any alarm text, reported temperature and appliances running at the time.
- Matching import-history data and details of recent tariff, software or equipment changes.
Sunergy Renewables is based in Nuneaton and supports solar and battery customers across Warwickshire, Leicester, Leicestershire and the wider Midlands. Contact us about your battery’s grid imports with those details so we can establish whether you need a settings review, a site investigation or a change to the system.
