Since I worked in the automotive electrical field for several years here's a subject that I can address with some authority.
First, let's discuss the function of the battery in any vehicle. It has only one purpose. To provide sufficient energy to start the vehicle! (Okay, before someone calls me on it, in modern vehicles it retains the memory in the computer. The amount of current needed for this task is so minuet that we can ignore it.) Once the vehicle is running the battery should just be sitting there getting recharged by the current left over from the tasks of operating the machine. All of the lights, the horn, the radio, the cell phone recharger, the nav system etc. should be powered by the charging system. Unfortunately, particularly on scooters the charging system has very little left for recharging the battery. If you've accessorized your scoot you may have problems. I once had a customer who complained that the battery kept dying in his car. The reason? He had installed a super whizzbang stereo with two humongous amplifiers in the trunk that drew, by themselves 105 amps against a 90 amp alternator. 
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1.
I've never worked in that field, but let me add at least few more major functions of the battery, except just providing initial kick to spin the engine.
- just as important, it filters out spikes in electricity produced by the alternator/charging system, thus protecting electrical circuits and various appliances in the vehicle (I am aware there is a separate filtering/regulating device in every vehicle for this too...)
- source of electric energy in case of overload imposed on the charging system (this happens rarely, but it can happen)
- a number of things, even on scoots, depend on battery to function. For example, car alarm, remote door opening, car radio memory. In case of scoots, it can be alarm, clock memory and certain injection functions in case of fuel injected scooters
2.
Furthermore, let me dispel the myth about undersized electrical charging systems on scoots.
One of the things I use on all my scoots are heated handgrips that use up to 5 A of electricity initially and then around 2-5 A.
I have heard even on this forum people who think it is impossible to fit those on scoots "because battery is too weak", "because the charging system cannot sustain that" etc.
In winter time, when I go to work and when I come back, I use both lights and heated handgrips. I commute 12 kms from suburbs, so most of the time I use long beam.
Never had a single issue, not on Beverly 200, not on People 250 S and even my gf who rides a "small" scoot - Agility 125 - never experienced ill effects.
This leads to conclusion that there are some Amps of spare capacity embedded in the charging system.
I guess that this myth originates from old mopeds and bikes from 60's and 70's that were less generously egineered in that
department.
p.s. This certainly does not mean that you can bake bread in under seat storage in oven connected to 12V outlet, but it should not be a problem to divide Watt output of the generator system with 12V and calculate total Amps it can take without problems.
My 5c.
