What's battery indicator say when you turn on your phone? Low battery or 100% charged...?
It could be the battery as John said, or it could be the charging port.
You can bring your phone to the nearest Koodo shop to send it for repair if it's still under warranty.
Generally, if more than a year old, batteries tend to lose their ability to hold a charge, or can only power the device for more than a few minutes. The symptom you describe points to a failing battery and a new battery should fix the problem.