The Rotax 912 only has a 20 amp alternator as standard - integral installation. An external belt driven 45 amp item is available.
I use to fly a Tecnam P2002-JF and after an hour in the circuit in 'poor' viz with nav lights, strobes, landing light (all non LED), GNS430, transponder and electric fuel pump on, we had the same situation with the 430 blinking off line when taxying in. The next day the battery (effectively a motorcycle battery) was flat, obviously drained whilst supporting the load.
Working things out afterwards, a standard non-LED landing lamp will draw 10 amps all on its own. By the time you add all the rest of the kit it is easy to see that the standard alternator cannot cope with what would be a normal load on Lycoming powered (65A alternator) machines. Have a look at a load sensing ammeter in a PA28 and see what load the alternator is putting out.
On the RV-12, we carefully calculated what the max load would be (a bit like Apollo 13....) before deciding on the final fit.
The other problem that can be encountered with the Rotax is looking after the voltage regulator. With the lighting kit on the RV-12, Van's supply a cooling shroud and blast tube for the regulator. Without this it will fail after a lengthy period of high load. The regulator did fail on the Tecnam after around 200 hours - it did not have a cooling shroud.