OK. I've had a look at the Rotax manual.
From what I can gather; the engine fitted to your aircraft has two sources of electrical power. The manual says they are both alternators. One; the 'internal generator' is fitted to supply power and triggering for the engine ignition, and an engine rev-counter. This alternator can supply 20 amps and the text says it has an external diode bridge to convert the 3 phase AC to DC. I should imagine that this "internal generator" is 'self exciting', i.e. needs no battery to operate. In other words, it's a bit like a magneto, and makes the engine electrically self contained.
The circuit around the "internal generator" also includes switches to cut the ignition circuits. It is these that would need to be switched on in order for the engine to start, and conversly how the engine is stopped - by switching them off. For aircraft which just need engine power to drive a propellor, this is all that is required. (e.g.powered hang gliders?)
If an aircraft has instrumentation which needs powering, and perhaps an electric starter; a battery and a second, "external alternator" can be fitted. This is similar (but smaller - only 40 amp) to the unit found on a car and has an internal diode bridge to convert the AC to DC for any circuits 'external' to the engine.
That's as much as I can glean. I hope it answers your question, and of course I stand to be corrected by any Rotax experts.
U