How to check a battery performance claim

Battery claims often rest on one number. This checklist sets out the questions to ask before repeating one. Each question has a short reason. Where a fact is given, its source is linked.

A note on sources

The facts below come from a US Department of Energy (DOE) page on vehicle battery research and the Vrulum methodology. The rest of the list is questions to ask, not facts about batteries.

The checks

1. Is the number for a single cell or a whole pack? Why: a figure for one level should not be compared with a figure for the other. Ask which level the number describes.

2. Is energy density given per kilogram or per litre, and for which level? Why: a figure per kilogram should not be compared with a figure per litre, and a cell figure should not be compared with a pack figure.

3. How many cycles, and what counts as the end of life? Why: the DOE page names increasing battery life as an aim of its battery development research (DOE), and a life figure means little without a stated end point. Ask for the number of cycles, the capacity loss that ends the count, and the test conditions.

4. Which charge rate sits behind the charging time? Why: a fast-charge claim with no stated charge rate cannot be checked. One of the goals on the DOE page is a target to decrease charge time to 15 minutes or less. That is a target, not a measured result (DOE).

5. Are efficiency and self-discharge measured, or estimated under ideal conditions? Why: a figure given only under optimal conditions may not match everyday use. Ask for the conditions under which the figure was measured.

6. What safety test or report supports the claim? Why: the DOE page says its vehicle battery research aims to improve batteries' ability to tolerate abuse conditions. A research aim is not a test result (DOE). Ask for the test standard, the test report and who ran it. Do not state a safety result in an article unless the report has been read.

7. Which Vrulum label does the claim deserve? Why: the methodology uses "Demonstrated" for a claim shown in a published experiment, test or shipping product, and "Reported, unverified" for a claim stated by a company or team but not independently confirmed (Vrulum methodology). Grants and patents are not evidence that a claim works.

8. When was the source published, and when was it last checked? Why: the methodology says every significant factual statement links to a specific source, with the date it was published and the date it was last checked (Vrulum methodology).

What to do with the answer

If the claim fails more than one check, describe it as unverified and say which check failed. If it passes, still state the scope it covers: the cell or pack level, the test conditions and the date. Do not turn a single quoted figure into a general statement about battery technology.