Polti Vacuum stick (working with a fault) (Halfway S20)

Are you good at repairing things? Then stop here!
I have an almost brand new Polti Vacuum, kept it as spare for long time. Then I started to use it and after just 1 and a half month showed a fault.
The vacuum works, however, it "stops" after 30-40 seconds despite battery being fully charged.
I don't want to dispose of it as it's almost new, if you re into electric things you might want to repair it and use it! It's free and you can give it a new life!
I'll give it with it's original charger and brush included.