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.