I have a discharged failed AGM battery that was sitting on the shelf for a couple of years because I keep forgetting to take it in to be recycled and it dried out, cracked itself open like an egg and spilled its white powdery innards out the bottom.
Normally, you can't overcharge them if they're connected to an alternator. But they can still overheat and have the same problem. Or if they had a faulty,cracked, or damaged cell to begin with, I suppose you COULD overcharge it with an alternator because the remaining cells won't be able to hit 12V combined and instead will just burn off all their fluid and bulge trying to take more voltage than they can handle.. In any case, always check a battery to make sure it's at least 12V resting voltage without any charger plugged into it before putting it in a car. If it's 10V disconnected resting voltage, it might have a bad cell and take it back to the store! A battery with a bad cell will never hit 12V resting voltage without bulging, boiling or venting.
I have a discharged failed AGM battery that was sitting on the shelf for a couple of years because I keep forgetting to take it in to be recycled and it dried out, cracked itself open like an egg and spilled its white powdery innards out the bottom.
how are you supposed to not overcharge them if its connected to an alternator
Normally, you can't overcharge them if they're connected to an alternator. But they can still overheat and have the same problem. Or if they had a faulty,cracked, or damaged cell to begin with, I suppose you COULD overcharge it with an alternator because the remaining cells won't be able to hit 12V combined and instead will just burn off all their fluid and bulge trying to take more voltage than they can handle.. In any case, always check a battery to make sure it's at least 12V resting voltage without any charger plugged into it before putting it in a car. If it's 10V disconnected resting voltage, it might have a bad cell and take it back to the store! A battery with a bad cell will never hit 12V resting voltage without bulging, boiling or venting.