Apple customer goes to the top for iPhone battery answer
The head of Apple's operating system iOS confirmed that open but unused apps do not affect iPhone battery life after a customer emailed boss Tim Cook.
The customer from Ohio, known as Caleb, asked Mr Cook whether closing down "multitasking apps" improved battery life and whether it was something the chief executive did himself.
Senior vice-president Craig Federighi replied "no and no".
However, other smartphone batteries can benefit from app closure.
Microsoft advises Nokia Lumia owners to close apps that aren't in use on a web page about extending battery life.
Android creator Google suggests identifying and closing apps that are not often in use but warns that frequent use of its Overview device manager to do this will in itself drain the battery.
"You can view and optimise your device through closing running apps and uninstalling unnecessary apps," said Samsung in an announcement about a new "smart manager" app for the Galaxy 6.
While many Apple users do shut down apps in the belief it extends the iPhone battery this is not advice explicitly given by the firm itself.
It only recommends disabling apps from carrying out background refreshes in a list of tips about saving power.
The BBC has contacted Apple for comment.
Former chief executive Steve Jobs would sometimes reply directly to unsolicited emails - generally in very few words - but Tim Cook appears to be less forthcoming.
Caleb shared his unusual correspondence with the website 9to5mac.
"On a technical level, most of the apps are either frozen in RAM or not running at all, the system just displays them as a history for consistency. This is why the battery life impact is negligible," reporter Benjamin Mayo notes.
Caleb himself appears to be surprised by the attention the emails received.
"That went more viral than I thought it would," he tweeted.