Anyone considering a home battery soon comes across two families: the plug-in home battery that you plug into a socket, and the fixed home battery that an installer builds into your electrical installation. Both store electricity, but they differ considerably in power, installation and cost structure. This guide sets out the differences side by side.
In brief
- A plug-in home battery works through a fixed socket and mainly covers your base load.
- A fixed home battery is built into your installation and can deliver higher power.
- In Flanders, a fixed storage system requires an AREI inspection; a plug-and-play device does not (Fluvius, accessed 27/09/2026).
- The choice depends on your consumption profile, your installation and how much building work you are willing to do.
Power
The biggest difference is in power: how many watts the battery can deliver at once. A plug-in battery is connected to a household circuit. Synergrid reports that plug-and-play devices are in principle limited to 2,600 W, and that regional authorities advise, for safety reasons, limiting the combined inverter power to 600 to 800 W; in Flanders, registration is mandatory from 800 W (Synergrid and Fluvius, accessed 27/09/2026). Many plug-in models are therefore set to 800 W through the socket by default.
A fixed home battery has its own connection and can deliver higher power. For fixed storage systems in Flanders, Fluvius states a limit of 5 kVA for a single-phase connection (Fluvius, accessed 27/09/2026). Heavy consumers such as a heat pump or an EV charger can therefore be covered to a greater extent by a fixed battery than by a plug-in model.
Capacity
Capacity (kWh) and power (W) are two different things. Plug-in systems also come in larger capacities, some expandable with modules. The power through the socket then determines how quickly that energy becomes available. So a large plug-in battery delivers for a long time, but not a lot at once. You can read how to determine the right capacity in how many kWh do I need.
Installation
Plug-in
You place the device in a suitable spot, plug it into a fixed socket and connect a meter. Synergrid explicitly asks you not to use an extension lead and to plug directly into a fixed socket (Synergrid, accessed 27/09/2026). A dedicated circuit is recommended. If in doubt, leave work in the fuse box, such as fitting current clamps or a new circuit, to an electrician. Details in safe placement and connection.
Fixed
An installer builds the battery and the inverter into your installation, provides the necessary protection devices and registers the system. The installation is then inspected according to the rules of your country or region.
Inspection and registration
In Flanders, Fluvius regards plug-and-play devices as appliances: no inspection is required. Fixed storage systems do require an AREI inspection (Fluvius, accessed 27/09/2026). Registration with the grid operator may be required for both, depending on power and region. In Belgium, a plug-in device must also be on the Synergrid plug-and-play list; check this per model at the time of purchase. Read rules in Belgium or rules by country for other countries.
Cost structure
We don't give any amounts here, as they depend on the model and the installer. The structure does differ, however:
| Cost item | Plug-in | Fixed |
|---|---|---|
| Device | Battery and inverter, often in one device or in modules | Battery, inverter and possibly a separate controller |
| Meter | P1 or CT meter, sometimes sold separately | Usually included in the installation |
| Installation | Limited, possibly a new circuit by an electrician | Labour by an installer |
| Inspection | Not required in Flanders according to Fluvius | In Flanders, an AREI inspection |
| Expansion | Modules or additional units, depending on the system | Depending on the system, via the installer |
So don't just compare the price of the device, but the total of what you need to get it into your home safely and working. The savings calculator lets you enter that total cost.
When does which one suit?
A plug-in home battery often suits if
- you mainly want to cover your base load in the evening and at night;
- you don't want any alterations to your installation;
- you rent or want to be able to take your battery with you when you move;
- you want to start small and possibly expand later.
A fixed home battery often suits if
- you have heavy consumers that you want to power from the battery;
- you are having a new solar installation fitted and want to arrange everything in one go;
- you want backup power for a larger part of your home;
- you have a three-phase installation and want to spread the power across the phases.