Discharge rate on car batteries

[popalock]

Going to change my car battery, but as the battery is still sort of ok, I wanted a more precise way of determining when a battery needs to be replaced.

Obviously if the voltage drops quickly over time, the battery has to be replaced. But how quickly?

All batteries will have a natural decay rate, but what drop in voltage from 12.6v over how many hours is the point at which the battery should be replaced?

Googled it, couldn't find an answer

 

[balge]

Depends on the size and type of battery, parasitic loads, all sorts I would have thought

Besides, the Voltage is not that important, cold cranking Amps is what you need to test for starting

 

[Ted]

To test a battery it needs to be fully charged.
Then a load test needs to be done on it.
All batteries self discharge to a degree, but not to the extent that it will determine if the battery is good or bad.