There is a "Battery Usage" option in the Settings app on your iPhone or iPad; select the General subsection, then Usage. Turning on the "battery Percentage" option will display the remaining battery power as a percentage in your menubar. Sounds like a cool option, right? Well, we often advise that people do NOT turn on this feature. For some reason, people feel a level of anxiety when the percentage of available battery is presented to them.
If after 1 hour your battery percentage has decreased from 99% to 84%, that is actually within normal real-world range of use. However, the numerical percentage makes it appear artificially significant. If all that was displayed was the icon, you'd only observe a small visual change to the icon.
So, if you're the type to set your clock ahead by 15 minutes, double check the stove before you leave, or obsessively apply Purell to your hands, then do yourself a favor and do not enable the Battery Percentage option.