Give the name and battery number so we can look up what you have. You can use them but we don't know the capacity. The good news is that wheelchairs typically use top quality deep cycle batteries because they live a hard life and must be absolutely reliable.
Most wheelchairs are 24 volt systems and use two 12 volt batteries. They use all different sizes with group 24 usually the largest.
My son is a wheelchair mechanic. I get free used gel 12v group 24 batteries from him whenever I want a replacement set. They swap them out of chairs every 18 months.
The ones he gets me are MK Battery (Deka) by East Penn Manufacturing. They are heavier than a typical flooded group 24 with slightly less capacity but they are free to me. Originally they cost over $200 each.