Make sure you know the correct charger for your scooter. You can find this in the manual or on the existing charger.
For the best use of batteries, only charge the mobility scooter once the battery dial gets down by halfway. This allows the batteries to have a bit of a cycle. Simply using the scooter on a short trip and then charging it is called 'overcharging' and it can cause the batteries to depreciate quicker than via normal use. Always unplug a scooter from the wall after 48 hours. Never leave one on charge, even if the manual says you can, we've found over the years that the internal resistor does not prevent trickle charging and can overcharge your scooter.
Don't forget that overloading your scooter, driving over grass and hilly areas can cause the batteries to die a little quicker.