A home battery is a stationary battery energy storage system installed in a house to store electricity and release it when needed, either from rooftop solar panels or from the grid. In the climate & energy part of the smart home, it is the component that shifts energy in time: it charges when power is cheap or abundant and discharges when it is expensive or unavailable.
A home battery consists of battery modules, a battery management system and an inverter, and is usually controlled by software that responds to solar production, household consumption and electricity tariffs. Typical residential systems store 5 to 20 kWh, enough to cover a household’s evening and overnight consumption.
How a home battery works
A home battery works by converting alternating current (AC) from the home or grid into direct current (DC) for storage, then converting it back to AC when the house needs power. The battery management system (BMS) monitors the voltage, current and temperature of each cell group, balances them and protects the battery from overcharging or deep discharge.
The controller decides when to charge and discharge according to an operating mode. In self-consumption mode, surplus solar power charges the battery instead of being exported, and the battery covers demand once production falls. In tariff-based mode, it charges during low-price hours of a time-of-use tariff and discharges at peak times.
The following table describes the key parameters that define a home battery.
| Parameter | Typical range | What it determines |
|---|---|---|
| Usable capacity | 5 to 20 kWh | How much energy can be stored |
| Continuous power | 3 to 10 kW | How many appliances can run at once |
| Round-trip efficiency | About 85 to 95 percent | Energy lost in a charge cycle |
| Cycle life | About 4,000 to 10,000 cycles | Lifetime under daily use |
| Depth of discharge | 80 to 100 percent | Share of capacity usable without harm |
| Warranty | Typically 10 years | Guaranteed remaining capacity, often 60 to 80 percent |
Battery chemistry and system architecture
Most new home batteries use lithium iron phosphate (LFP) cells, which offer long cycle life, good thermal stability and no cobalt. Some earlier systems used nickel manganese cobalt (NMC) cells, which store more energy per kilogram but are more sensitive to heat. For a wall-mounted battery, weight matters less than safety and longevity, which explains the shift to LFP.
Systems are also classified by how they connect to the solar installation. A DC-coupled battery shares a hybrid inverter with the solar panels and charges directly from their DC output, while an AC-coupled battery has its own inverter and can be added to an existing solar system.
| Architecture | Efficiency from solar | Best suited to | Main drawback |
|---|---|---|---|
| DC-coupled | Higher, one conversion fewer | New solar installations | Tied to a compatible hybrid inverter |
| AC-coupled | Slightly lower | Adding storage to existing solar | Extra inverter and conversions |
| All-in-one unit | Depends on design | Simple installations | Less flexibility in expansion |
Backup power and grid interaction
Not every home battery provides backup power during a grid outage. Grid-connected systems must disconnect from the grid when it fails, a protection called anti-islanding, and only systems with a transfer switch or backup output can keep supplying the house. Backup may cover selected circuits such as the refrigerator, lighting and router, or the whole home if the inverter power is sufficient.
| Backup type | Coverage | Switchover | Typical use |
|---|---|---|---|
| No backup | None during outages | Not applicable | Pure cost optimization |
| Emergency outlet | One or a few sockets | Manual | Basic resilience |
| Critical loads panel | Selected circuits | Automatic, short interruption | Refrigerator, heating pump, network |
| Whole-home backup | Entire house | Automatic | Areas with frequent outages |
Home batteries can also take part in demand response and virtual power plants, where an energy supplier or aggregator controls many batteries together to support the grid in return for payments or lower tariffs. This requires a reliable connection and clear rules about minimum reserve levels for the household.
Integrating a home battery into the smart home
A home battery delivers the most value when it is coordinated by a home energy management system (HEMS) together with the solar inverter, heat pump, electric vehicle charger and smart meter. The HEMS can decide whether surplus solar energy should charge the battery, heat water through a solar diverter, or charge the car, based on forecasts and prices.
- Solar forecasting avoids filling the battery from the grid at night when a sunny day is expected.
- Load shifting moves dishwasher or laundry cycles to times when the battery or solar can supply them.
- Reserve settings keep a share of capacity, often 10 to 30 percent, for outages.
- Open interfaces such as Modbus or a local API allow integration with home automation platforms.
Sizing, economics and common mistakes
Correct sizing depends on evening and night consumption, not on the size of the solar array alone. A battery that is too large stays partly empty for much of the year, especially in winter, while one that is too small fills by noon and leaves surplus to export. A common rule of thumb is to size usable capacity close to the average consumption between sunset and sunrise.
| Mistake | Consequence | Better approach |
|---|---|---|
| Oversizing for winter | Unused capacity most of the year | Size for typical spring and autumn nights |
| Assuming backup is included | No power during outages | Confirm backup output before purchase |
| Ignoring tariff structure | Weak financial return | Model savings with real tariffs |
| Poor installation location | Heat or cold reduces lifetime | Install within the rated temperature range |
Financial return varies strongly with electricity prices, feed-in compensation and subsidies. Where exported solar power earns little, batteries pay back faster; where net metering credits exports fully, the economic case is weaker and resilience often becomes the main reason to invest.
Explained without jargon
A home battery is a large rechargeable battery for your house. It fills up when there is spare electricity, for example from solar panels at midday, and gives it back later in the evening when the sun has gone down.
It works much like a water tank on a roof: you collect water when it rains and use it when you need it. Some home batteries can also keep the lights on during a power cut, while others are only designed to save money on electricity bills.
A typical use case
A family with a 7 kWp rooftop solar system exports most of its midday production for little payment and buys electricity in the evening at a much higher price. They add a 10 kWh LFP battery with a hybrid inverter and a critical loads panel for the refrigerator, heating circulation pump, lighting and router.
From spring to autumn, the battery covers almost all evening and overnight consumption, and grid purchases fall by roughly half over the year. During a four-hour winter storm outage, the critical circuits keep running from a 20 percent reserve, and the family barely notices the interruption.