Why does my battery stop discharging while it still has charge left?

The remaining energy may be reserved rather than unavailable. Many battery systems maintain a minimum state of charge so energy remains available for backup or battery protection.

Backup reserve

Fronius explicitly documents a Reserve Capacity setting: in normal grid-connected operation the battery does not discharge below the configured reserve. Other platforms use similar concepts such as backup reserve, minimum SOC or emergency reserve.

Fronius reserve-capacity documentation →

What this looks like in practice

If a 13.5 kWh usable battery is configured to preserve a large share for outages, the app can show substantial stored energy while the house starts importing from the grid. That can be correct behaviour rather than a battery fault.

Reserve versus peak shaving

There is a genuine trade-off. A higher reserve improves the energy held for a potential blackout but reduces how much is available to avoid evening peak imports. A lower reserve increases daily tariff utilisation but leaves less stored energy waiting for an outage.

Do not confuse reserve with target SOC

A charge target defines where charging should stop. A minimum/reserve SOC defines how far discharging is allowed to go. Some systems expose both, and a TOU schedule may also add its own target or power constraint.