How to compare commercial battery storage quotes
Two quotes at the same price per kWh can describe different batteries. A checklist for comparing usable capacity, power, scope, exclusions and warranty.
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Two quotes for a commercial battery can carry the same price per kWh and describe different equipment, different scope and different risk. The published figures in our guide to commercial battery storage cost show how wide the ranges are, and the reason is largely what each quote leaves in or out. This post is the checklist for putting quotes on a like-for-like basis before you compare a single price.
Step 1: agree what the kWh and the kW mean
A per-kWh price is only meaningful if everyone is dividing by the same kWh. Ask each bidder to state four numbers in writing:
- Nominal energy, the figure on the battery’s datasheet, in kWh.
- Usable energy, what you can actually draw after the manufacturer’s limits and any reserve, in kWh, and whether it is measured at the battery or at the point of connection after the inverter.
- Continuous power, in kW at the AC output, and whether it can be sustained for the whole duration.
- Duration, which is energy divided by power. A 250 kWh battery rated at 125 kW is a two-hour system.
Our guide to kW vs kWh explains the difference between power and energy, and why a battery sized on the wrong one disappoints.
Step 2: an example of how the ranking can flip
These are invented round numbers to show the arithmetic. They are not quotes and not typical prices.
| Quote A | Quote B | |
|---|---|---|
| Price before VAT | £90,000 | £92,000 |
| Nominal energy | 250 kWh | 240 kWh |
| Price per nominal kWh | £360 | £383 |
| Usable share of nominal | 90% | 95% |
| Usable energy | 225 kWh | 228 kWh |
| Price per usable kWh | £400 | £404 |
| Includes groundworks and enclosure? | No | Yes |
Quote A looks about 6% cheaper per nominal kWh. Per usable kWh the gap has shrunk to about 1%, and Quote B includes groundworks and an enclosure that Quote A would add as an extra. Comparing on the headline number would have picked the wrong bidder.
Step 3: a scope checklist
Ask each bidder to mark every line as included, excluded or provisional. A quote that cannot be marked up this way is not yet a quote.
| Item | What to ask |
|---|---|
| Battery modules and racks | Capacity, chemistry, manufacturer and model |
| Inverter (power conversion system) | Rating, efficiency, and whether it is the right size for the kW you need |
| Battery management and energy management software | What it does, who operates it, and whether it needs a subscription |
| Enclosure or container | Indoor or outdoor, rating, and whether it is included |
| Switchgear, protection and cabling | Whether your existing board can take it, or the upgrade is priced |
| Groundworks and civils | Base, fencing, screening and access, for outdoor installations |
| Fire detection, suppression and ventilation | What the design is based on, and who signs it off |
| Metering and monitoring | What data you will see, and who owns it |
| Grid connection | Who applies, who pays the network operator, and what happens if reinforcement is required |
| Commissioning and handover | Which tests, which documents, and what training |
| Planning support | For outdoor installations, who prepares and pays for any application |
| Operation, maintenance and warranty | What is covered, for how long, and what voids it |
Step 4: performance and warranty terms
Headline efficiency and life claims are where optimism creeps in. Ask what each figure is measured on, and put the answers beside a neutral benchmark. The US National Renewable Energy Laboratory’s 2024 Annual Technology Baseline uses a round-trip efficiency of 85% and a 15-year lifetime at about one cycle a day for commercial batteries (NREL ATB 2024). That is a modelling assumption, not a promise, but a bidder claiming far better should be able to show the basis.
- Round-trip efficiency. Measured at the battery or at the AC point of connection, at what power and temperature?
- Warranty. The length in years, the energy throughput or cycle count it covers, the capacity it guarantees at the end, and what conditions void it.
- Degradation. How much capacity the warranty allows you to lose, and how it is tested.
- Availability. Whether any uptime is guaranteed, and the remedy if it is missed.
Step 5: price basis and risk
- Fixed or provisional? A fixed price for the whole scope, or provisional sums for civils and connection that can rise.
- The grid connection. The network operator’s offer sets the connection charge. Ask what happens to the price if the offer includes reinforcement. Our page on the G99 application explains the process.
- Payment milestones. How much is due before equipment is delivered, and what protection you have if the supplier fails.
- Programme. Which dates depend on the supplier and which on the network operator.
Questions to ask every bidder
- What is the usable energy at the AC point of connection, and the continuous power, in writing?
- Which items in the scope checklist are excluded or provisional?
- What is the total price including every exclusion you know you will need to add?
- What is the warranty throughput, the guaranteed end-of-warranty capacity and the conditions that void it?
- Who applies for the grid connection, and who bears the cost if reinforcement is needed?
- Who maintains the battery, and what does that cost per year?
- What happens to the price, the warranty and the monitoring if the installer or the manufacturer fails?
- Are you MCS-certified, NICEIC-registered or a member of another body, and what is the registration number? Check it with the issuing body.
If you would like quotes from installers that meet your own checklist, the free feasibility summary sets out your load and a sensible size so that every bidder starts from the same figures.
Sources
- National Renewable Energy Laboratory, Annual Technology Baseline 2024, commercial battery storage
- Commercial battery storage cost on this site, with the published UK bands and their sources
Get the numbers for your own site
This guide is general. The only figure that matters is yours, modelled from your own consumption and tariff.
What you get, within 3 working days: a 2-page battery feasibility summary naming your indicative system size (kW and kWh), the installed cost band, which value streams actually apply to your site (peak-shaving, red-band DUoS avoidance, load shifting, solar self-consumption, grid services), and an honest payback range. If storage does not stack up for your site, the summary says so.
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Published by SEO Dons, a specialist commercial energy information network. We are independent: we are not an energy supplier and not a battery manufacturer.