Based on anecdotal observation, many iPhone users have long believed that older iPhones get slower over time. Generally, people have assumed that this is because of new features and additions in new versions of iOS that are better optimized for the latest phones.

But Reddit users, and Geekbench developer John Poole, have a compelling new theory, backed up by benchmarks: the iPhone may throttle performance to preserve battery life or avoid unexpected shutdowns as the battery degrades.