Battery indicator accuracy: what should reviewers test?

For devices that only have a few indicator levels, what is the fairest way to test whether the indicator is actually useful?

I do not expect laboratory precision from three lights. I mainly want the warning to arrive consistently enough that the remaining runtime is not a surprise.

Consistency is the key. I look at whether the indicator changes at repeatable points, whether the low-battery warning leaves enough time for normal use, and whether charging status is unambiguous.

It also helps to quote the manufacturer description accurately so the review does not imply more precision than the product claims to provide.

A consistent warning threshold is more useful to me than pretending the display is a fuel gauge.