Home battery not charging or discharging

What it usually means

Home batteries are the most heavily automated equipment in a house, and that is why they generate so many complaints that turn out not to be faults. A battery does not decide for itself when to charge and discharge — it follows a strategy, and that strategy may come from the manufacturer's app, from an energy tariff that controls the battery in exchange for a cheaper rate, from a schedule someone set months ago, or from a combination of all three. The first job is not diagnosis but reading: find out what the system has been asked to do today.

Tariffs are the biggest single cause. A time-of-use tariff will often charge a battery from the grid overnight at a low rate and hold that charge for the evening peak, which means a battery that appears to ignore a sunny afternoon is doing exactly the right thing commercially. Some suppliers go further and take direct control, dispatching the battery for their own balancing purposes, so it can charge and discharge at times that make no sense from inside the house. If your battery behaviour changed the week your tariff changed, you have your answer.

The second cause is the reserve. Nearly every battery has a minimum state of charge it will not go below, kept back so that it can carry the house through a power cut. Set that reserve high — some people set it to fifty per cent after one bad winter — and the battery will refuse to discharge most of what it holds, which reads exactly like a fault: full charge, no output. In an outage the same setting is what allows the system to keep the lights on, and knowing the number is the difference between a complaint and a decision.

Then the physics. Batteries have a usable capacity smaller than their nameplate, lose output in the cold if they are in a garage or an outbuilding, and charge more slowly when nearly full. A battery that seems to hold less than it used to may be showing normal degradation over years, or simply being measured against the wrong figure. Winter is also when generation is lowest and consumption highest, so a battery that never fills between November and February is usually short of solar rather than faulty.

Genuine faults do exist and they announce themselves differently: a specific named alert in the app, a light pattern the manufacturer publishes, an internal breaker reported as open so the unit cannot store energy, or an inverter fault. Those are worth reporting rather than resetting, and the wording of the alert matters because manufacturers use distinct names for distinct conditions. What matters more, on this equipment above all, is where the investigation stops. If the battery is part of a solar system, isolating it does not make the roof wiring safe — the panels generate whenever it is light, and there is no switch that changes that.