Batteries are a nuisance in any application: they are always flat, people are always giving you different advice depending on the chemistry of the batteries (always charge this one, run this one down etc.) and- before you know it- you have to replace them again... and they're not cheap. There are a few misconceptions about scooter batteries that I would like to clear up.
The first thing is that almost all scooters have two 12v batteries. There are one or two machines out there with three, but you will almost always have at least two. A lot of people will physically look at their scooter and say 'there is only one' because that is what they lift off the machine (the 'battery pack'). Though almost always upon opening this pack you will be greeted with two 12v batteries.
Secondly, scooter batteries LOVE being charged up. Keep them topped up, that is all you have to know. You cannot overcharge them- but you can undercharge them. If you leave scooter batteries for approximately a week (depending on factors) they will self-discharge. If you then leave them for 2 - 3 weeks you will begin to permanently lose distance. Two months of this treatment will render your batteries virtually useless- sure, they will switch the scooter on, but you will only get 500m before you will lose power.
Generally when you buy a new scooter they will come standard with basic batteries. These batteries are great for average use (10km use every 2nd or 3rd day, person weighs approx. 80kg, no 'nose-bleed hills etc.) but if you stress them too much you would be advised to buy 'heavy-duty batteries'. Lots of scooter owners scoff when asked whether they want heavy-duty batteries like it is a useless up sell. The reality is that there are chemical and physical differences between batteries such as amount of lead, gel or lead acid, over-all amperage to case size (two batteries, same case, one is 12amp the other 14amp). If you are using your machine a lot, you are heavy, travel up serious hills or great distances, I do recommend thinking about a battery upgrade. Otherwise you may find yourself forking out for a new set before too long... with your thumb out on the side of the road!