A specification sheet is a set of claims, and knowing which ones carry qualifiers is most of what reading it well consists of.
Capacity needs a unit that travels
Watt-hours compare across voltages; amp-hours do not, and milliamp-hours at cell voltage least of all. Where a maker publishes a usable figure alongside a nominal one, that is a sheet worth trusting further.
Power needs a duration or a load
A surge rating without its duration, a runtime without its load, a noise figure without its distance: three of the most commonly published numbers on this shelf, and none of them means anything alone.
Cycle life needs two reserves
The depth of discharge tested and the capacity the pack must still hold at the end. Both change the headline enormously, and a maker publishing several figures at several depths is showing its working rather than hiding it.
Panel ratings need their test conditions
Peak watts are measured under defined conditions that do not occur outdoors. The temperature coefficient and the degradation figure are the numbers that describe behaviour over a life, and they get far less attention than the wattage.
What is not on the sheet at all
The battery management system current limits, the idle consumption of an inverter, whether firmware can be updated, whether a battery can be replaced, whether a declaration of conformity can be obtained. A maker that publishes these is telling you something about how it expects the product to be used, and for how long.
What people ask before they order
What does a missing qualifier usually mean?
That the figure was chosen from the most favourable conditions. It is not necessarily dishonest, but it makes the number incomparable with one that was qualified, which is the practical problem.
Which single figure is most often misread?
Capacity in milliamp-hours, because it is counted at cell voltage rather than at the output voltage. Converting to watt-hours removes the ambiguity and makes two products comparable.
Last reviewed 16 September 2026