Is it OK to replace a flooded battery with an AGM battery in an older model car?

This forum contains a lot of electrical expertise, including automotive electrical. So I'm going to ask this question here in the hopes of getting informed answers. I've searched Google and Jeep forums extensively and have been getting conflicting info about this for years.

My 99 Jeep Cherokee XJ and 97 Buick Park Ave are older cars that orignally came with flooded batteries. Is it a good upgrade, or a bad idea, to replace their G34 flooded battery an G34 AGM Odyssey battery? If it matters, Odyssey use pure lead for the plates.

Elsewhere on the Web advice is conflicting and I have no idea who to believe. Some says it's fine. Some say it's an upgrade. Some say my old school alternator will overcharge AGM batteries and shorten battery life. Some say it will under charge. Some say it's fine. Some say AGM would be an improvement for me.

What's the truth here?

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Edited in Later: I just found the following at Odyssey battery website, which may be relevant.
Is 14V the max my Jeep or Buick alternators are likely to put out? If so, I'm guessing it's OK to use an Odyssey AGM battery in those cars. But I don't know for sure. So advice still appreciated.

AGM batteries can generally take more of a beating in off road situations, so it may be an advantage in the Jeep. As far as charging characteristics, I've never heard about any difference. AGM stands for absorbed glass mat, basically meaning that the acid/electrolyte is soaked up by a fiberglass mat that fills the space between the lead plates. It is still a lead acid battery, so I don't know how it would be affected any differently than a normal lead acid battery. If you really want an upgrade, get an Optima. I've heard that some manufacturers alloy their lead with things such as arsenic and antimony, I believe, to help prevent sulfation of the plates, iirc. One thing I look for in a new battery is dual posts. It can be really handy to have side posts and top posts for jumper cables and adding accessories.

I previously read that AGM batteries can be damaged by overcharging by cheap battery chargers that may charge at 16 to 17 volts during top of phase.

However, I just read my Schumacher 3 stage battery charger's owners manual online and learned it goes no higher than 14V during the last/finishing (topping off) phase of charging, I also read at Odyssey website that Odyssey AGM can handle up to 14V during the finishing/topping-off phase of charging.

So my portable charger should be OK for compatibility?

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I read at Odyssey's website that their AGM batteries are fully charged at 12.84V. Are my Jeep and Buick late 90s alternators compatible with keeping a battery charged to 12.84V?

Agm replacement will be just fine. I've replaced all SLA and flooded batteries with AGMs and have had better than no issues..... Espc in the winters.

Most car batteries have been maintenance free for years and have similar charging requirements to AGM. They have gas recombination that works well as long as you don't heavily over charge them. Pure flooded batteries can be overcharged as you can add water that is lost. This can be a benefit to prevent sulfation. Long life stationary storage batteries are still flooded for this reason. They can last longer than AGM but they take maintenance.

AGM should be fine. But ALL batteries can be damaged by overcharging. Some of the small "trickle chargers" are not really regulated, so do not just blindly leave them on as maintainers. Given time, they can fry an 8D truck battery.

I usually have an "expendable" battery around the place, not too worried about brief overcharging. I'll put any unknown charger on it for 24 hours or so, then check voltage. Then I make a sticker for the charger, showing final float voltage. My favorite charger is still an old Heathkit 10 amp that tops out around 13.5 or 13.6 volts. That charger CAN maintain a battery all winter without cooking it. But I buy maintainers (BatteryMINDer or Battery Tender) for that purpose.

Charley3 said:

I just found the following at Odyssey battery website, which may be relevant.

The below is part of Oddysey's recommendations for using a battery charger with their AGM batteries.

Make sure the charge voltage at the battery terminals does not
exceed 14.0V (charge from battery charger).

A fully charged ODYSSEY battery will
read 12.84V, which verifies a full charge.
​

Is 14V the max my Jeep or Buick alternators are likely to put out? If so, I'm guessing it's OK to use an Odyssey AGM battery in those cars. But I don't know for sure. So advice still appreciated.

Click to expand...

Follow the guidelines from Odyssey. Do not exceed 14.0V (at the specified battery temperature, typically 68 degF). Charge voltage can be higher at colder temps, and should be lower at higher temps. AGM batteries are more susceptible to thermal runaway from over charging than are flooded batteries.

The label on my Exide Edge AGM battery specifies a maximum charge voltage of 14.2V-14.6V. Charging temp is not noted on the label. My alternator tops out at around 14.9V at 20degF.

Choose an AGM battery that will not be overcharged by your vehicles charging system.

Almost any car or truck charging system is going to produce and its' electrical system is going to see peaks in the 14.2 - 14.4 range. All SLA's, AGM's are made to handle this Voltage. AGM's and SLA's are completely interchangeable.

"Older car" is in some ways a relative term, but I'm not sure it applies here. A '97 is not an "older car" in the same way a '65 or a '43 is. Charging from an alternator is also different from charging from a charger. I'd be more careful about charger selection than which car I'd install it in.

You could always ask the battery maker for a go/no-go on your intended application.