BAT usage before expiration

Ok, I received a reward of 15 BAT

it tells me that they will expired on 8/15/19. My question: What can I do with these 15 BAT? I have to donate it? Because I would like to keep them, how can I do ? If it’s not possible, when ?

(Vous pouvez me répondre en français pour ce qui le parle)

The free BAT drops are meant to be used on the system, so by donating them, yes, that’s why they are free.
The ones you earn by watching ads are your own and you’ll be able to transfer them to yourself in the future.