A worked example
Why do battery cells fade faster in the heat?
Follow the question through competing explanations, a calculation and a finding. Keep the observation separate from the cause.
Keep the explanations open.
Compare electrolyte breakdown, lithium plating and SEI growth. An appealing explanation is still a hypothesis.
Give the investigation a scope.
Ask Felix to compare the two temperature groups. Inspect the method and the inputs behind the calculation.
Review the finding, then choose.
Lower capacity retention is an observation. It does not establish the cause. Keep that limit visible and choose a better test.