Mobility Scooter Batteries (Netley Abbey SO31)

Hi I have a mobility scooter that I'm trying to sort for a family member, I think the batteries are gone no power 5v held charger but I know charge is going on . Wondering if anyone has some scooter batteries they can sort me out with please, these are. 12v 35ah batteries. Any help would be greatly appreciated as batteries are not that cheap.