Did you know you can check your iPhone battery from your Mac? Well, you can. Here’s how:
Make sure your Mac and iPhone are both using the same iCloud account and have Bluetooth enabled.
Hold down the Option key and click the Wi-Fi icon in the Mac menu bar. After a second or so, your iPhone will show up in the Personal Hotspot section even if you’re not using it to set up a personal hotspot. If you’re not using it as a personal hotspot, that option will be in light grey; if you are using the iPhone for that purpose, Personal Hotspot will be in bold letters.
The battery icon and signal strength is display. However, if you mouse over your iPhone's line, a small menu will appear that shows the exact percentage of battery you have left.
(This how-to is based on my experiences and info on Apple's support pages — where the images sometimes come from.)