5 kWh home battery costs: when smaller storage makes sense

Is 5 kWh enough?

It depends on the loads you want to move. Five kWh could represent several hours of modest household demand, but it is not a promise that a particular home will run through an evening. A heat pump, electric cooking or vehicle charging can change the picture quickly.

For an illustrative load of 0.5 kW, 5 kWh divided by 0.5 kW gives ten hours before allowing for reserve, losses and changing demand. That arithmetic says nothing about whether the battery is wired to support the home during a power cut. Backup needs a suitable system design.

A public cost reference, with limits

The Energy Saving Trust’s battery guidance gives around £4,600 as a reference for a 5 kWh battery system. Treat this as a broad published guide, not an offer from Home Energy Compare or an independently sampled local average. Your inverter, installation location and electrical work can change the total.

A second small module may be cheaper to add within one installation than fitting a complete new system later. Conversely, buying expansion capacity “just in case” can be poor value if demand is unlikely to grow. Request both the initial cost and the future expansion conditions.

Why the cheapest box may cost more to fit

A battery-only listing may exclude the inverter, controller, mounting equipment, commissioning and protective devices. An apparently dearer package may contain those items. Ask who is responsible for compatibility when components come from different manufacturers.

• Confirm the usable capacity rather than adding nominal module labels.
• Check charge and discharge power, especially for short cheap-rate periods.
• Confirm indoor or outdoor location requirements and available space.
• Ask what remains under warranty if another installer expands the system.
• Check whether the quote includes backup, and which circuits it supplies.

Check the marginal value of more capacity

Compare two scenarios using the same energy rates. If an extra 5 kWh of storage only allows you to shift another 1 kWh on a typical day, value the extra 1 kWh, not the nameplate expansion. Charging losses and foregone export payments still apply.

Use the battery scenario tool to test a smaller and larger capacity. Keep daily shiftable demand unchanged first. This makes it easier to see when extra capacity stops adding value.

If you do not have solar, start with our battery-without-solar guide. If backup is the main reason for buying, read the power-cut guide before comparing prices.