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What is a domestic battery?
A domestic (home) battery is a rechargeable battery installed at your property that stores electricity for use later. Most modern home batteries use lithium-ion cells — the same broad family of technology found in phones and electric cars — housed in a sealed unit about the size of a small cabinet.
Alongside the battery sits an inverter. Batteries store electricity as direct current (DC), but your home runs on alternating current (AC), so the inverter converts between the two. Some systems build the inverter into the battery unit; others use a separate box.
Two numbers worth knowing
- Capacity (kWh) — how much electricity the battery can store.
- Power (kW) — how quickly it can charge or discharge.
Storing electricity: charging and discharging
Charging
Electricity flows into the battery — from the grid, or from solar panels if you have them — and is stored.
Holding
The battery keeps the energy until it’s needed.
Discharging
Stored electricity is released to power your home or, in some arrangements, sent back to the grid.
Repeat
The cycle repeats, usually daily, managed automatically.
No battery is perfectly efficient: a small amount of energy is lost each time it charges and discharges, mostly as heat.
Smart battery controls
A smart battery doesn’t just fill up and empty at random. Software decides when to charge and when to discharge, based on things like the time of day, electricity prices and signals from the wider system. You don’t need to press any buttons — it runs in the background.
How a smart home battery might run over a day. The battery charges overnight when demand is typically lower, holds its charge through the day, and discharges during the early-evening peak when demand is typically highest.
Why electricity is worth more at some times than others
Demand for electricity rises and falls through the day. It is typically highest in the early evening, when people get home, cook and switch on lights, and lower overnight. Supply changes too — wind and solar output depends on the weather.
Smart meters can record half-hourly consumption, which makes it possible for suppliers to offer smart tariffs where the price changes by time of day. GOV.UK notes that these tariffs let consumers save money by using energy away from peak times or when there is excess clean electricity available. A battery lets a home do this automatically: store electricity when it is cheaper or plentiful, and use it when it is expensive or scarce. Read more in can a home battery reduce electricity bills?
Get a smart battery installed at no cost
Homeowners and private tenants can apply.
Grid-connected batteries and the electricity system
Great Britain’s electricity system operator, NESO, works to make sure supply meets demand every second of every day. Government and Ofgem’s smart systems and flexibility plan describes smart technologies and flexibility as essential to integrating low-carbon power onto the system.
One home battery is small. But thousands of connected home batteries, managed together, act like distributed energy storage — soaking up electricity when there is plenty and releasing it when it is needed. That can help the system stay balanced and make better use of renewable generation. This is the idea behind the Free Home Battery Scheme: lower household bills, support for the grid and stronger energy security.
Solar-connected batteries vs other battery arrangements
Solar + battery
The battery stores surplus electricity your solar panels generate during the day, so you can use it in the evening. It can often also charge from the grid.
Standalone (grid-charged) battery
No solar panels needed. The battery charges from the electricity network — typically when demand or prices are lower — and discharges when they are higher.
Our guide to home batteries without solar panels goes into the difference in more detail, and the benefits of battery storage covers what they mean for households. For a broader overview, see our article on home energy storage.