Check 1 · Capacity
Nameplate vs usable
A quote states a nameplate energy figure (kWh), but a battery never delivers all of it. Usable energy is what is left after the allowed depth of discharge, the reserve held back for health, and round-trip losses. Ask for the usable kWh at the duty you actually need — not the label on the rack. A system sized on nameplate can be 15–25% short once you discount to usable energy.
★ Key takeaway — Size on usable kWh, not the nameplate on the rack — the gap can be 15–25%.
Check 2 · Power
Power vs the duty
Energy is only half the sizing; power (kW) decides whether the battery can cut the peak at all. If your worst peak is tall and brief, you need power more than energy; if it is long and flat, you need energy to ride it out. A quote that leads with kWh and is vague on continuous kW — and on how long the battery can hold that kW — has not been matched to your load's actual peak shape.
★ Key takeaway — A quote vague on continuous kW (and how long it holds) was not matched to your peak.
Check 3 · Degradation
Degradation and the warranty floor
Cells fade with cycles and calendar age, so the saving in year one is not the saving in year ten. Ask what end-of-warranty capacity is guaranteed (often around a 70% floor), on what cycle and temperature assumptions, and whether the quoted payback uses the degraded capacity or the day-one number. A payback built on day-one capacity quietly overstates the return across the asset's life.
★ Key takeaway — Make the payback use degraded, end-of-warranty capacity — not the flattering day-one number.
Check 4 · Derating
Temperature, inverter, efficiency
Datasheet numbers are measured in ideal conditions. Real output is derated by ambient temperature, inverter limits and round-trip efficiency. Confirm the savings are computed on the net energy the system delivers at your site's conditions, not the gross figure on the datasheet — the two can differ by a tenth or more.
★ Key takeaway — Savings should be on net energy at your site's conditions, not datasheet-ideal gross.
Check 5 · Response
Response time vs the event
Shaving a demand peak means reacting inside the interval that sets the charge. If the control loop is slow, the meter has already logged the peak before the battery responds. Ask how fast the system detects and dispatches against a rising peak, and whether that is fast enough for the half-hour (or shorter interval) your tariff bills on.
★ Key takeaway — If the control loop is slow, the meter logs the peak before the battery reacts — ask for the response time.
Check 6 · Assumptions
The assumptions behind the saving
Every quoted saving rests on a control method and a set of tariff assumptions. Which method is assumed — constant power, a fixed threshold, or an adaptive one — and does it match how this load behaves? What tariff, what price spread, what escalation and discount rate, and who chose them? A saving produced by a favourable method on an optimistic tariff is a modelling choice, not a result.
★ Key takeaway — A saving is only as good as the control method and tariff behind it — ask which, and who chose them.
Check 7 · Independence
Who sized it — and who profits
The last question is the one most buyers skip: is the party that sized the system and produced the saving the same party that profits from selling it? That is not an accusation, it is a conflict to manage. An independent check — sizing and savings validated by someone with no stake in the hardware — is the cheapest insurance on a six- or seven-figure decision.
★ Key takeaway — If the party sizing the system also profits from selling it, get an independent check — it's cheap insurance.
In practice
How EWISER uses this checklist
This is the structure behind the EWISER Fingerprint audit: an independent review of a vendor's quote against your own load — capacity, power, degradation, derating, response time, revenue, payback and warranty — so you learn what the quote assumed before you sign, not after the system is commissioned. EWISER does not sell the battery; it checks the one you have been offered.
★ Key takeaway — The EWISER Fingerprint audit runs this whole checklist against your own load — before you sign.
Frequently asked questions
What's the single most common flaw in a BESS quote?
Sizing on nameplate rather than usable energy, paired with a saving built on day-one capacity. Both flatter the return. Discounting to usable energy and degraded capacity is the quickest reality check.
Do I need my load data to check a quote?
It helps a lot. Many quote assumptions — power vs duty, the control method, the achievable shave — can only be tested against your actual interval load. Without it, a quote is a model of an average site, not yours.
What does an independent audit cost?
EWISER's independent audit (the Fingerprint Match) is 15 credits and includes the full investment-grade report plus the vendor-quote review. The same credits also unlock a project's reports.
Request an independent audit →