A LITTLE-KNOWN number on your iPhone reveals if your handset has a serious problem.
If you fall foul of the “rule of 80”, it might be time to cough up some cash.
It’s all linked to your iPhone battery and its health over time.
When you charge up (and through use, discharge) the battery in your iPhone, it degrades.
Over time, your iPhone will hold less charge compared to when it was new.