2001 5.4

[Boose]

Ok. I'll feed that into my knowledge base about batteries. However the original statement was too extreme. I would never buy a new battery because the alternator failed and I kept driving the TRUCK until it wouldn't run anymore. I only replace batteries if there is good evidence that its degraded. Like ... a battery tester says its no good anymore. Or it won't hold a charge or the voltage drops too low while cranking or other things. I always give a battery a chance to prove itself but when its not up to ***** it needs to go.

And I think it depends on how much of a discharge the battery was subjected to. If it only goes to 8V ... I wouldn't think that would be too traumatic. If its shorted to ground and run down to 2V then that's worse. But I'm just guessing

Also ... What happens that ruins a battery if it discharges? There has to be some physical phenomenon that transpires. What is it? Does it matter if its an AGM battery or any other technology ... Like a marine battery?

There are significant differences in the lead alloys that make up the plates in a starting battery vs. a deep cycle. AGM & Gels add another layer of complexity. A starting battery contains higher levels of calcium when compared to a true deep cycle. This allows the higher cranking amps for turning over an engine. A deep cycle has a higher lead content which allows the repetitive discharge/recharge cycles and reserve capacity. If you completely discharge a starting battery such as the one in your truck, the chemical reaction that takes place causes the plates to harden a bit. Do this more then once or on an older battery and it will never come back. It would come back voltage wise for a while but the cranking amps would decrease significantly (think run stereo, turn on headlights but only click the solenoid when you turn the key)

 

[rjdelp7]

Here are a few things to check. Check your CD changer for a stuck CD or magazine. Its wired 'hot' and will continue work with key off. Hook up a small bulb, between the neg terminal and cable. If it lights up, you are drawing current. Jump the solenoid, at the firewall with a screwdriver. If it turns over, you can trace your way back. Check for a bad ground, at the battery. We had work truck die and gauges went nuts. It was a loose/bad connection at the battery. A burned out charge/batt light in the cluster, will prevent the alternator from working. Check to see if it lights up, when key is turned.

 

[Bilsto]

I think when batteries get old, sulfates start to build up between the plates and that causes trouble. I worked at an auto parts store many years ago, but my memory of that problem has faded. But when you start getting sulfation, you'll usually notice that the battery starts to swell.