Laptop given as collateral and now its mine..but i got a question.?

My brother gave me a laptop that was left as collateral to him. The owner of the laptop has not come back to claim it and it has been a year since the agreed deadline. So know the laptop belongs to me. I believe that the battery is going bad because it runs out of power fast. How would I be able to check if this computer is still under warranty (for a new battery) even though I am not the original owner? The model of this computer is a HP Pavilion DV5000.