Bad Batt

I bought my mother what id hoped to be a long lasting product but was let down to hear her 24 volt cordless trimmer battery is dead and wont charge. It was a gift and I know now about registering these tools but here I am with a total loss when still under warranty. I run a contracting company and have learned u get what u pay for but this was lithium and new technology and your name isnt new so I am sad to see im on the receiving end of a bad deal. Trimmer was awesome and I bragged it up to all I could but now feel dumb and cheated. Any advise? That is besides making sure I regester everything?