Windows 10 typically displays a battery icon in the notification area, also known as the system tray, when using a laptop or tablet. This icon shows the current battery percentage. Here's how to reset it if it disappears.
Your battery icon may still be in the notification area, but "hidden". To look for it, click the up arrow to the left of your message icons on the taskbar.  If you see the battery icon here (an area that Microsoft calls the "notification area overflow window"), simply drag and drop it back to the notification area on the taskbar.
If you do not see the battery icon in the hidden icon panel, right-click the taskbar and select "Taskbar Settings."
You can also go to Settings> Customization> Taskbar instead.
Scroll down the Settings window that appears and click "Turn system icons on or off" in the Message area.
 Find the "Power" icon in the list here and switch it to "On" by clicking on it. It will also appear on your taskbar.
You can also switch to or from other system icons here, including Clock, Volume, Network, Input Indicator, Location, Action Center, Touch Keyboard, Windows Printer Space, and Touch Pad. 
RELATED: How to customize and tweak your system tray icons in Windows  If the power option here is gray, Windows thinks 10 that you use a desktop computer without battery. The taskbar's power icon will not appear on computers without battery.
Even after you reset the battery icon it does not show an estimate of remaining battery life when you mouse over it. Microsoft has disabled that feature, probably because it is generally inaccurate. ” width=”650″ height=”220″ src=”/pagespeed_static/1.JiBnMqyl6S.gif” onload=”pagespeed.lazyLoadImages.loadIfVisibleAndMaybeBeacon(this);” onerror=”this.onerror=null;pagespeed.lazyLoadImages.loadIfVisibleAndMaybeBeacon(this);”/>
How to activate remaining battery life in Windows 10