Sorry with diodes, nil way to physically tell or even by loading them. It appears the heavy duty ones are arcing out to short (closed circuit) vs going open circuit. Thus the battery feeds the coils and drains to zero volts.
The reason why the electrical goes haywire is the alt starts feeding AC and DC along the circuit and things chuck a wobbly. The batt absorbers some of the AC danger but suffers badly from the experience.
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