American and French officials want to know why Apple has intentionally slowed down older smartphone batteries.

Story so far: In December, following uproar on Reddit and analysis by Geekbench, Apple admitted that it throttles iPhone performance to overcome problems caused by aging or otherwise janky batteries. It also offered customers battery replacements for $29 rather than the usual $79.

Questions remain: The Wall Street Journal notes that governments don’t appear to be convinced by the company’s explanation. French officials conducting an investigation into the throttling have called it “programmed obsolescence.” The chair of the U.S. Senate Commerce Committee sent a letter to Apple asking questions about the implications for consumers.

Expensive mistake: Eroding consumer trust could hurt Apple. Barclay’s has estimated that battery upgraders shunning new handsets could put a 16-million-unit dent in iPhone sales this year—equating to as much as $10 billion in lost revenue.