I agree with Oldguy,about the battery taking a surface charge, but you did not say how old the battery is, or if you have any other devices drawing voltage from the battery. Also, Ive seen low milage on a machine but time killed the battery from sulfation-not enough use/charges. Here is a test to check how good the battery is.If you charge the battery fully, put it in the scooter and hook it up. Then hook up a voltage meter to the terminals. (See the chart below) While starting (or attempting to start)the scooter watch the voltage. If the voltage drops to less than 10 volts while the starter is turning the engine over, the battery is bad and needs to be replaced.(probably has a bad cell from sulfation) Each cell represents 2+volts. That is why you see 6 fill caps on a battery. A new charged maintenance free battery should show about 12.9-13.0 volts. Here is a chart for maintenance free battery voltage, percentage of charge
12.9-13.0 volt 100% charge
12.6-12.8 volt 75% charge
12.3-12.5 volt 50% charge
12.0-12.2 volt 25% charge
11.9 or less 0% charge
Kind of decieving looking isn't it. but this is out of the book information. A Regular (non-maintenance free battery ) usually runs about .3 to .4 of a volt less on the chart. Now you say- what about that draw down when starting?, pulling the battery down to around 10 volts? well it takes alot of amps to crank over that engine-especially cold, so the voltage drop is normal, but a good battery will usually not drop below 10.5 volts while cranking the engine over. This is why the electronic stuff( CPU, electronic fuel injection,etc) operates on 9 volts, so every thing will work like it is supposed to while starting. Hope this information helps in the future. This information applies to cars, motorcycles, and the like that is equipped with a 12 volt battery