Why is your battery charging from the grid? Usually a setting doing exactly what it was told.

Usually a setting rather than a fault. The most common cause is your backup reserve being set above the battery's current charge level — the system treats the reserve as a safety floor it must reach, so it imports to get there, and on many systems it will do this even with grid charging switched off. Other normal explanations: you are in a virtual power plant that has its own separate reserve setting (setting the household reserve low does nothing if the VPP one is still high); a severe-weather feature such as Tesla's Storm Watch has charged the battery to full ahead of a forecast storm; you are on a time-of-use or wholesale tariff with scheduled charging deliberately filling the battery on cheap power; the battery is refilling to its reserve after an outage or deep discharge; or solar simply cannot fill it in winter. Only once those are excluded is a genuine fault likely, most often a CT clamp fitted incorrectly.

Five common reasons, and most are configuration. The battery may already be sitting at its reserve level — if it shows 20% and the reserve is 20%, there is no energy it is permitted to use, so it holds. A virtual power plant may be holding the charge for a market event rather than releasing it to your household. Your evening load may exceed the battery's maximum continuous power output, which is a separate specification from its storage capacity, so the battery supplies what it can while the grid covers the rest — that is a power limit rather than a fault. The system may be in backup-only or storm mode, which deliberately holds charge. And some systems restrict discharge in cold conditions to protect the cells. Check the reserve level first, then the VPP settings (remembering there can be two separate reserves), then the operating mode.

Three explanations, two of which are intentional and profitable. The most common is a virtual power plant event: your VPP is discharging your battery into the grid at a moment of high wholesale price or system need, and paying you for it — check your VPP app's event history to confirm. The second is deliberate arbitrage on a wholesale or pass-through tariff, where discharging into a price spike earns considerably more than the stored energy is worth to your household. The third is configuration: some systems have an explicit export-from-battery setting that can be enabled during commissioning without the owner being told. It is genuinely wrong when you are not in a VPP, not on a wholesale plan, and the battery is exporting at a low feed-in tariff — in that case you are effectively selling stored energy for less than it cost to store, and it is worth raising with your installer as a specific misconfiguration.

Almost always deliberate, and usually saving you money. If you are on a time-of-use tariff with a cheap overnight or super-off-peak window, or on a wholesale plan, a correctly configured system will fill the battery when power is cheapest and discharge it during the expensive evening peak — which frequently beats waiting for tomorrow's sun, particularly in winter when solar cannot fill the battery anyway. The other common cause is the backup reserve: if the reserve sits above the current charge, the system imports overnight to reach it. Virtual power plant programs may also charge your battery from the grid as part of their operation, and severe-weather features charge to full ahead of a forecast storm. If none of those apply and you would rather it only ever charged from solar, most systems have a grid-charging toggle — though be aware that on many, reserve-topping overrides it.

Four patterns that settings do not explain. Repeated offline periods, usually a communications problem such as weak wifi to the inverter, a changed router password or a failed dongle — not dangerous, but it blinds your monitoring and can cost VPP payments. A sudden step change in usable capacity between one month and the next, as distinct from the gradual fade that is normal ageing. Recurring error codes, alarms, or an isolator that keeps tripping, which is the system reporting a problem rather than a nuisance to reset around. And numbers that do not add up — solar generating, low household consumption, battery not charging, or import and export that look swapped — which often indicates a CT clamp fitted backwards or on the wrong conductor, a common commissioning error that quietly costs money because everything appears to work. Any burning smell, swelling, visible damage or unusual heat means isolate if safe and call your installer immediately.

Screenshots, taken while the behaviour is actually happening. Capture the live energy-flow screen showing solar, house, battery and grid at the moment the odd behaviour occurs, with the timestamp visible. Then capture your settings pages: the backup reserve level, the current state of charge, the operating mode, the grid-charging toggle, and any virtual power plant configuration including its separate reserve if it has one. Add the app's event or alert history if the system logs one. Note the date, time and weather, since storm-related charging and winter solar shortfall are both common explanations. This matters because a vague report gets a slow, generic response, while a timestamped screenshot showing, for example, grid import at 2am with the reserve set to 30% usually gets diagnosed on the first call. Contact your installer first, then the manufacturer — and if your installer has ceased trading, your consumer guarantees survive them.