Is a commercial battery main-rate or special-rate plant?

Our guide to capital allowances on battery storage gives the rates and a worked example, and leaves one question open: whether a commercial battery is main-rate or special-rate plant and machinery. This post is the evidence trail behind that question. It sets out what we searched, what we found, and what we could not find, so that you can take the right questions to your adviser.

Why the answer matters

For spend inside your Annual Investment Allowance (AIA) it does not matter at all, because HMRC’s manual lets the taxpayer allocate the AIA to any type of plant and machinery, special-rate spend included. Above the £1 million a year cap it matters a great deal. A company gets full expensing, a 100% deduction with no cap, on main-rate plant. On special-rate plant it gets a 50% first-year allowance, with the rest written down at 6% a year. Main-rate plant that is not fully expensed is written down at 14% a year from April 2026.

Where we looked

We checked these primary sources on 7 October 2026:

• The statute. Section 104A of the Capital Allowances Act 2001 (the definition of special-rate expenditure) and section 33A (the list of integral features).
• HMRC’s Capital Allowances Manual. The three pages on integral features (CA22310, CA22320 and CA22330) and the page on the annual investment allowance and special-rate spend (CA23084).
• GOV.UK guidance. The pages on full expensing and the 50% first-year allowance, and on writing-down allowance rates and pools.

We searched the raw text of the three integral-features pages for the words battery, batteries, generator, uninterruptible and standby, and found none. We also searched for an HMRC page on electricity storage specifically and did not find one.

We then read what installers and suppliers publish on the subject. The pages we read disagree. Some tell businesses that a commercial battery qualifies for 100% full expensing. At least one states the opposite, with equal confidence, and says anyone claiming full expensing is wrong. None of them cited a provision of the Act or a page of HMRC’s manual for the classification they gave. If the people selling batteries cannot agree, the sources are the only safe place to start.

The special-rate list, item by item

Section 104A(1) lists what counts as special-rate expenditure. Taking each item in turn:

The only item that could capture a battery, and the only one that turns on the facts rather than on the label, is the integral features entry.

The integral-feature reading

Section 33A lists five integral features: an electrical system (including a lighting system), a cold water system, a space or water heating system or a powered system of ventilation, air cooling or air purification, a lift, escalator or moving walkway, and external solar shading. Electricity storage is not named.

HMRC’s manual says “electrical system” is not defined in the legislation and takes its ordinary meaning: a system for taking electrical power from the point of entry to the building or structure, or generation within it, and distributing it through the building. It adds that the term does not include other building systems intended for other purposes, and gives communications, surveillance and alarm systems as examples.

Those words support two readings, and we do not think either is established.

• For special-rate. A battery that is wired into the building’s low-voltage distribution, and discharges into the circuits that serve it, can be described as part of the system that takes power in and distributes it through the building.
• Against. The statutory list is of building services. A battery that is operated as a business asset, to move energy between tariff periods, to earn flexibility revenue or to keep processes running, serves the business rather than the building. A containerised unit outside the building, feeding the site through a connection, is also not obviously “within the building or structure”.

This is analysis, not HMRC’s view, and a different adviser might weigh the facts differently. The point is that the text of the manual does not resolve it.

The long-life reading

Long-life assets are items with a useful life of at least 25 years when new, and spending on them above £100,000 in an accounting period goes to the special-rate pool. The only published planning assumption we found for a commercial battery is NREL’s 2024 Annual Technology Baseline, which models a 15-year lifetime at about one cycle a day. That is a cost-model assumption and not a legal test, but it is well short of 25 years. A battery could still meet the test if its design life were substantiated at 25 years or more, so the manufacturer’s documented design life matters.

What this means in practice

• Mixed projects need classifying item by item. Solar panels are named special-rate expenditure. A project with panels and a battery can therefore have two different answers.
• Allocation can help. Because the manual lets the taxpayer choose how to allocate the AIA, an adviser can direct it at special-rate items first and leave main-rate items for full expensing, which has no cap. That makes classification matter most when the AIA is used up.
• Full expensing has conditions beyond classification. The expenditure must be on or after 1 April 2023, the asset must be new and unused, and it must not be bought to lease to someone else, apart from background plant in a building.

Questions to put to your adviser

1. Do you treat a battery of this kind, connected in this way, as main-rate plant, as an integral feature or as neither? On what basis?
2. If you rely on a provision of the Act or a page of HMRC’s manual, which one?
3. Have you seen this classification challenged by HMRC for storage?
4. Can you show the outcome both ways for this project, with the cash-flow difference?
5. How should the contract split groundworks, enclosure, plant and electrical connection so that each can be classified?

What would change our answer

A statement in HMRC’s manual or a Business Brief that names electricity storage, a tribunal decision on a storage installation, or an amendment to section 33A or section 104A would settle it. We will update this post and the tax guide if we find one. If you know of a published HMRC position that we missed, send it through the contact page. For readers new to the equipment itself, what a BESS is explains the parts that sit behind the question.

Sources

• Capital Allowances Act 2001, section 104A and section 33A
• HMRC Capital Allowances Manual, CA22310, CA22320, CA22330 and CA23084
• GOV.UK, Check if you can claim full expensing or 50% first-year allowances
• GOV.UK, Writing down allowance rates and pools
• National Renewable Energy Laboratory, Annual Technology Baseline 2024, commercial battery storage