The exciter coil produces 100-300V AC when the engine spins. The CDI stores this, then releases it to the ignition coil when the pickup coil sends a signal. No battery power is needed for spark.
A parasitic drain is likely happening through the Red wire circuit (unswitched power) or a faulty regulator/rectifier that is bleeding power backward to ground. suzuki gn125 wiring diagram
This applies to most GN125 models (early 90s to late 2000s). Differences exist for kick-start-only vs. electric start, and some markets have different lighting switches. The exciter coil produces 100-300V AC when the engine spins
: Steps up low voltage from the CDI to a high-voltage spark for the spark plug. suzuki gn125 wiring diagram