Hi,
Here are two options to try, if you haven't already done so.
1. Go to Control panel > Device Manager, scroll down to Network Adapters, click on + symbol to expand tree, right click on the WiFi network adapter listing and click on Properties. Click on the Power Management tab then uncheck the box next to Allow the computer to turn off this device to save power then click OK.
If you are running Win 10 the quick way to get to Device Manager is to press the Win key + x key together, an option box will appear on the left side of the screen, find and select the link to Device Manager.
See if this solves the problem.
2. If the above doesn't solve the problem then this link details how to modify the laptop's power plan settings, when running on battery power, to enable the WiFi network adapter to remain on. It explains what to do for all Windows OSs from Vista through to Win 10. Try Methods 2 or 3
If you are running Win 10 the quick way to get to Power Options is to press the Win key + x key together, an option box will appear on the left side of the screen, find and select the link to Power Options.