A/c charging vs dc charging

[zanekeimigdesigns]

This may have been asked before but why is it that you have to have a charger specifically for agm and gel batteries but your vehicles alternator charges all battery types? Is it just the difference between a/c and d/c charging?

[ShadeTreeMechanic]

The alt won't correctly charge an AGM or gel cell. Here is the deal. When a lead acid battery is charged it gives off hydrogen gas. The deeper the battery was discharged, the more it will gas especially at a high rate of charge (now imagine a 250A alt). The AC charger with an AGM / gel mode tapers the rate of charge as it reaches capacity to prevent more gas from being formed than the glass mat or gel can absorb. Too much gas would cause the case to balloon and possibly leak. If you see an AGM case that looks all sucked in, its because the case vented and now it can get any air back in. If your AGM appears to have moisture on or around it that just won't seem to evaporate, its because its acid. Most of the time we can get away with an AGM on an alt because we don't usually deep discharge them and they tend to stay topped up. Guys with lots of batteries usually use a plug in onboard charger to top them up and keep them happy.

[Broke_Audio_Addict]

A charger that plugs into your wall is still charging the battery with dc voltage.