Here are the electrical specifications for your scooter.
It has a generator* to provide electrical power to the motor as well as charge the battery. The specifications state that is has a 6V 2AH battery (2AH =7200 Coulombs, that's what the 7.2kC means).
- Usually generators provide DC output while Alternators provide AC which is rectified to DC output.
Here is the link to the service manual for your scooter.
Try getting a SLA type battery - (sealed lead acid, maintenance free) - as long as you don't reach the gassing voltage / cell for it when it is being charged by the generator you should be able to use one and not have to worry about battery maintenance.
I think gassing voltage is approx 2.97V/Cell which equals 8.91V when charging a 6V battery. Check the following link if in doubt or my maths/logic is faulty.
The output of the generator varies from 5.5V at 2300 rpm to 8.7V at 8000 rpm so it just squeezes in.