The electrical system is abnormal.

Battery capacity is insufficient.  Electrolyte specific gravity or liquid level is too low;  

Short circuit between plates;  Plate magnetization;  Poor wire contact;  

Plate active substance off and so on, can lead to insufficient battery capacity.  

The generator does not generate electricity.  The main reason is disappearance of remanence;  

Magnetic coil disconnection;  Poor commutator contact;  Brush stuck inflexible;  

Short circuit between armature turns.