Diagnosis
Sounds like the rechargeable battery inside the handle has reached the end of its life. These batteries degrade over a few years.
How to Fix It
The battery is not user-replaceable on the Vitality. Your practical fix is to buy a new handle. They're often sold without the charger base. Before you do, make one last check: leave it on the charger for a full 24 hours. Sometimes a deeply drained battery needs a very long trickle charge to wake up. If it still dies in under a minute after that, the battery is gone.
If That Didn't Work
If the brush is relatively new and doing this, the charger base might be the issue. Clean the contacts as described in the first fix. A poor charge leads to weak performance.
Heads Up
Don't try to take the handle apart to replace the battery yourself. It's sealed with waterproofing and you'll likely break it or create a safety hazard.