The battery that enables starting of a car dies after some period of use but faults from other areas can shorten its lifespan. Examples are faulty alternator and bad battery terminals.
The main battery fuse of a car is a relatively high amperage fuse that protects the overall battery circuit. When it gets blown, it causes problems like no crank and other accessories not working.
When the high voltage battery of a hybrid car becomes weak, there is a significant increase in spending on gas due to fast drain and frequent recharge.
Faulty alternator, bad terminals, ground faults, bad cables are the main causes of low voltage output from the charging system to the battery of an automobile.
Current measurement is best done by clamping the conductor carrying the current instead of having an ameter in series. This method is good for measuring parasitic battery drain.
A cell or more than one cell in a Hybrid car's high voltage pack can get blown due to high electrical resistance and also due to the effect of high temperature.