Also See : How to Use WhatsApp on PC or Laptop
How to Expand Your Phone Storage with Wireless USB stick
Before using Google Drive backup make sure that you have the following things.
1. A activated Google Account.
2. Enough free Google Drive space for your WhatsApp chats and media.
3. Free space on your phone to create the backup.
Download the WhatsApp version 2.12.303 and open it. Go to Settings > Chats and calls > Chat backup > select Google Drive backup > select the frequency for backup. You will need to select Gmail account you are using for the backup. Tap on the Back up over to choose the network you wish to use for backup. I recommend you to use Wi-Fi connection for this purpose.
Make sure that you uses the same phone number and Google account used to create the backup to restore WhatsApp chats and media. The restore process is simple, you need to install WhatsApp on your new device and verify Your mobile number and enter email address. After verifying your number, you will be prompted to restore your message and media from Google Drive.
Also See : How to install Apps directly into Your SD card
Note : You can also delete your old WhatsApp files from Google Drive to save disk space. Go to Google Drive and login to your account. Click on the Gear icon in the top right > Settings > Manage Apps. Scroll down to find WhatsApp in the list and click on Options > Delete hidden app data.