Battery terms
Home battery storage terms, in plain words
Grouped by where you will meet them, with a link to the page that explains each one in context.
The pair that matters most
kWh is how much energy a battery holds; kW is how fast it can deliver it. Usable kWh, not the label size, is what to size and compare on.
| Term | Meaning | More |
|---|---|---|
| Usable capacity | The energy, in kWh, you can actually draw from the battery. Size and compare on this. | Read |
| Nominal capacity | The label size in kWh. MCS records it and official statistics count it; usable is usually a little lower. | Read |
| Continuous power | How much the battery can supply at once, in kW, for as long as it has energy. | Read |
| Round-trip efficiency | The share of energy put in that comes back out, as a percentage. | Read |
| Warranted throughput | The total energy, often in MWh, the warranty covers; sometimes given as cycles. | Read |
| Cycle | One full charge and discharge, or the same amount of energy spread over partial ones. | Read |
| Term | Meaning | More |
|---|---|---|
| Inverter | Converts between the direct current of panels and batteries and the alternating current your home uses. | Read |
| AC-coupled | A battery with its own inverter, joined on the home side; leaves an existing solar inverter in place. | Read |
| Hybrid inverter (DC-coupled) | One inverter for panels and battery together; on a retrofit it usually replaces the old one. | Read |
| Backup (EPS) | Switching that separates the home from the grid in a cut, so the battery can run chosen circuits. | Read |
| Reserve | The share of the battery kept back from daily use, to protect the cells or for a power cut. | Read |
| Term | Meaning | More |
|---|---|---|
| PAS 63100 | The 2024 specification on protecting homes from battery fires: where a battery may go and what it needs. | Read |
| ESQCR regulations 21 and 22 | The 2002 safety rules on switched sources and sources running alongside the network. | Read |
| G98 and G99 | The two routes for telling the network operator: notify within 28 days, or apply before installing. | Read |
| MIS 3012 | The MCS installation standard for battery storage, separate from the one for solar panels. | Read |
| Statement of conformity | The installer's written confirmation that the work follows PAS 63100, attached to the electrical certificate. | Read |
| Term | Meaning | More |
|---|---|---|
| Time-of-use tariff | A tariff with cheaper and dearer hours that a battery can work around. | Read |
| Smart Export Guarantee (SEG) | The arrangement under which suppliers pay for exported electricity, at rates above zero. | Read |
| Typical domestic consumption values | Ofgem's reference figures for yearly household use, revised from 1 July 2026. | Read |
| Self-use (self-consumption) | The share of a year's solar used in the home rather than exported. | Read |
Missing a term you met in a quote? Send it through the contact page and we will add it. The references behind these definitions are listed on references.
What this page is based on
- PAS 63100:2024, fire protection for battery energy storage in dwellings (BSI, sponsored by DESNZ), PDF (read 3 Nov 2026)
- Electricity Safety, Quality and Continuity Regulations 2002, regulation 21 (switched alternative sources) (read 3 Nov 2026)
- Electricity Safety, Quality and Continuity Regulations 2002, regulation 22 (sources running in parallel with the network) (read 3 Nov 2026)
- MCS guidance for installers on telling the network operator (G98 and G99) (read 3 Nov 2026)
- MCS Installer Operating Requirements (2026), technologies and use of the MCS mark, PDF (read 2 Nov 2026)
- Citizens Advice: choosing an energy tariff (fixed, variable, time-of-use and Economy 7) (read 3 Nov 2026)
- GOV.UK guide to the Smart Export Guarantee (read 3 Nov 2026)
- Ofgem decision on typical domestic consumption values (May 2026, in use from 1 July 2026), PDF (read 3 Nov 2026)
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