Originally Posted By: TheLoneRanger
I read that a battery should be replaced when the voltage drops to 12.4v on a fully charged battery.
Is this true?
No... there's a lot more to it than that - like if the battery is dropping to 12.4V (with no load), is it REALLY fully charged? Automatic/smart chargers will almost never FULLY charge a lead acid battery - nor will your alternator. Put it on a manual charger @ 2-6 amp mode for about 8hrs and THEN see what the voltage holds at. Otherwise, if the battery is still dropping down below 12.5 (again - with NO LOAD) then the plates have likely shed too much lead sulfate and there's no way to put it back and make it part of the battery again. Go easy on the manual charging though - if your specific gravity goes too far north of 1.27ish (about 12.65-12.7 resting voltage) you start increasing rate of corrosion due to higher acid concentration (either from charging or evaporation/electrolysis)
otherwise, all batteries fail eventually. Getting a battery load test is a good indicator of health though. Forget about the small electronic testers - they're only a best guess. If you want to test a battery for cranking amps AND capacity you need to do a full 15 second load test at 50% of the battery's rated CCA. Anything else (aside from the fancy electronic bench testers at AZ and similar stores) is just an indication of it's ability to start the car IF the battery is fully charged - which, big fudgin deal, I can figure that out by turning the key. I wanna know if it's gonna hold it's charge parked overnight.
Finally, if your battery is dropping to 12.4 installed in the vehicle, then that's acceptable. I'd be more interested in a reading after 24 hours of sitting.
I read that a battery should be replaced when the voltage drops to 12.4v on a fully charged battery.
Is this true?
No... there's a lot more to it than that - like if the battery is dropping to 12.4V (with no load), is it REALLY fully charged? Automatic/smart chargers will almost never FULLY charge a lead acid battery - nor will your alternator. Put it on a manual charger @ 2-6 amp mode for about 8hrs and THEN see what the voltage holds at. Otherwise, if the battery is still dropping down below 12.5 (again - with NO LOAD) then the plates have likely shed too much lead sulfate and there's no way to put it back and make it part of the battery again. Go easy on the manual charging though - if your specific gravity goes too far north of 1.27ish (about 12.65-12.7 resting voltage) you start increasing rate of corrosion due to higher acid concentration (either from charging or evaporation/electrolysis)
otherwise, all batteries fail eventually. Getting a battery load test is a good indicator of health though. Forget about the small electronic testers - they're only a best guess. If you want to test a battery for cranking amps AND capacity you need to do a full 15 second load test at 50% of the battery's rated CCA. Anything else (aside from the fancy electronic bench testers at AZ and similar stores) is just an indication of it's ability to start the car IF the battery is fully charged - which, big fudgin deal, I can figure that out by turning the key. I wanna know if it's gonna hold it's charge parked overnight.
Finally, if your battery is dropping to 12.4 installed in the vehicle, then that's acceptable. I'd be more interested in a reading after 24 hours of sitting.