AGM vs traditional flooded battery

[Argess]

I've been thinking of replacing my battery with an AGM one, however I'm not sure if my 1960s style Ford alternator and regulator will over or undercharge it and from what I understand, AGM batteries are susceptible to damage from this. Opinions welcome. T-Y.

ps: I can't seem to find a battery with end tabs to suit the mounting and those J-hooks with wing-nuts look they will be a pain to fiddle with under the fender, so I'll stick with a 24F7 and use a strap around the battery and tray.

[Sycraft]

if the output of the alternator is too high, you will shorten the lifespan of the AGM. I would not spend the additional money on an AGM in our application unless it was a modern powerplant with a charging system that adjusts output as needed.

[KarlzEE Bebout]

I run an AGM in my ERA because I don't want to have to check the fluid level. I have to remove the RR wheel to access the battery compartment. I run just a one wire 100a alternator with its internal regulator and have not had any issues. My 2¢.


BTW I should have mentioned that I have a 289 FIA, hence the RR wheel well battery location, I was not aware that the ERA 427 bodies had a different battery location.

[DanEC]

I use a cutoff on my under-hood acid flooded battery and just replaced it after 10 years. It is a pain to replace through the wheel well but every 10 years isn’t bad. - except I’ll be 80 then, bummer.

[Argess]

I was mostly interested in the AGM as it is maintenance free and won't spill if tipped over. The battery in my ERA is under the right front fender. You have to take the valve cover off to remove or install it. For installing it, the battery slips in at an angle and finally gets in place on its side. Then you rotate it upright. Checking the water level of at least 3 of the cells is difficult too. So the issues are similar to Karl's.

As I can no longer find the proper 24F7 battery with the hold-down side tabs, I'm free to choose something else, so I was investigating the AGM batteries but research showed some issues, so I thought I'd ask here.

[KarlzEE Bebout]

DanEC, You've had very good luck with your battery, enjoy! Our Arizona desert is extremely harsh on flooded batteries. They have been greatly improved the last few years and now sometimes last more than 2 or 3 years as in the past.

[Mongoose930]

I am using a Deadnutson alternator with AGM batteries and I have had no issues in 3 years:
https://www.deadnutson.com/1965-1971...e-alternators/

In my limited experience, I think you need an AGM specific battery charger / tender for AGM batteries, but my standard alternator has worked fine.

[twobjshelbys]

Isn't the Optima Red Top AGM class? I ran a 2x6V configuration all the time I owned my Cobra and never had any alternator or other charging issues.

In addition the Optima I had in my Ford GT lasted over 7 years being on a Battery Tender. (The Ford GT battery is an Optima Red Top with a Ford label.)

[CJ428CJ]

I've been using the Optima 35R in my ERA with the battery under the right front fender. It does have the end tabs to allow the ERA provided battery hold down to be used (although I did have to put a spacer under the battery). I like it so much better than the old lead acid battery I used to use. The lead acid battery would "sweat" acid which would drip down and stain my stainless pipes. I've had the Optima for 3-4 years with no problems (and I use a 120A 1-wire alternator).

Chris

[Morris]

Originally Posted by twobjshelbys

Isn't the Optima Red Top AGM class? I ran a 2x6V configuration all the time I owned my Cobra and never had any alternator or other charging issues.

Same for KMP259 for and we use a single wire Alternator..

[Argess]

I’ve done a little more research and as far as I’m concerned, all those “positive” attributes of an AGM battery are all unfortunately outweighed by the following “negative” comments I found on the net:

1/ https://www.repairsmith.com/i/blog/agm-vs-lead-acid/

Flooded lead acid batteries are much more tolerant to overcharging than AGM batteries. The sealed aspect of AGM batteries makes them more prone to thermal runaway, which can be triggered by overcharging. Even if you discount thermal runaway, overcharging will shorten an AGM battery’s lifespan faster. So, when charging an AGM battery, use a regulated battery charger to control the voltage and current going into the battery.

Note: Thermal runaway is when a battery generates too much heat than it can dissipate. The battery will dry out and melt, release toxic chemicals, and cause fires or explode in extreme cases. Nearby batteries will be affected and may result in a domino effect.

2/ https://batteryuniversity.com/articl...-glass-mat-agm

As with all gelled and sealed units, AGM batteries are sensitive to overcharging. A charge to 2.40V/cell (and higher) is fine; however, the float charge should be reduced to between 2.25 and 2.30V/cell (summer temperatures may require lower voltages). Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell); a direct replacement with a sealed unit could overcharge the battery on a long drive.

AGM and other sealed batteries do not like heat and should be installed away from the engine compartment. Manufacturers recommend halting charge if the battery core reaches 49°C (120°F).

Yes, I’ve never heard of this happening, and I know many Cobra owners use an AGM battery, but I’m sort of a low risk fellow at times. Too bad though. I almost bought one.

[DanEC]

Argess - are you dealing with an ERA? If so you should be able to remove the battery through the wheel well after removing the tire and the liner panel, and without tipping. Possibly early ERAs didn’t have this feature - not sure.

[Sycraft]

That was my answer...... I work in the industry and deal with alot of batteries, do not even get me started on Optima batteries, I would never own one. Seen too many issues in applications.

Originally Posted by Argess

I’ve done a little more research and as far as I’m concerned, all those “positive” attributes of an AGM battery are all unfortunately outweighed by the following “negative” comments I found on the net:

1/ https://www.repairsmith.com/i/blog/agm-vs-lead-acid/

Flooded lead acid batteries are much more tolerant to overcharging than AGM batteries. The sealed aspect of AGM batteries makes them more prone to thermal runaway, which can be triggered by overcharging. Even if you discount thermal runaway, overcharging will shorten an AGM battery’s lifespan faster. So, when charging an AGM battery, use a regulated battery charger to control the voltage and current going into the battery.

Note: Thermal runaway is when a battery generates too much heat than it can dissipate. The battery will dry out and melt, release toxic chemicals, and cause fires or explode in extreme cases. Nearby batteries will be affected and may result in a domino effect.

2/ https://batteryuniversity.com/articl...-glass-mat-agm

As with all gelled and sealed units, AGM batteries are sensitive to overcharging. A charge to 2.40V/cell (and higher) is fine; however, the float charge should be reduced to between 2.25 and 2.30V/cell (summer temperatures may require lower voltages). Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell); a direct replacement with a sealed unit could overcharge the battery on a long drive.

AGM and other sealed batteries do not like heat and should be installed away from the engine compartment. Manufacturers recommend halting charge if the battery core reaches 49°C (120°F).

Yes, I’ve never heard of this happening, and I know many Cobra owners use an AGM battery, but I’m sort of a low risk fellow at times. Too bad though. I almost bought one.

[patrickt]

My last two Interstate Mega-Tron batteries have both lasted 7 to 8 years in my ERA and probably would have lasted longer had I not broken down and replaced them. And I performed no maintenance on them whatsoever during all that time. Never even looked at the water levels. I would occasionally peek at the terminals to see if there was an abundance of that funky white stuff on them, but there was never enough to warrant doing anything so that's it. I wouldn't replace the battery in there with anything else.

June, 2024 -- see update below.

[Argess]

I've had a similar experience Patrick. I think I got my Cobra on the road back in 1997 and have just now had my 2nd battery fail. Like you, I never checked the acid/water, however on this second battery, the level was down almost a half inch in each cell. That didn't do it any good even though it lasted a long time.

As previously mentioned, my issue has been all new batteries do not have the clamp down end tabs. Also manipulating the battery into the battery tray might result in spillage with a vented battery. (Dan: mine is an older ERA and doesn't have that access panel)

I have a strap and a parachute buckle to fix the first problem. I'll just have to check for chafing of the strap for a while. The latter issue is to go with a sealed flooded lead acid battery.

I still havn't completely given up on AGM as so many people claim success, and to be truthful, I can't see an extra 1/2 volt from the alternator/regulator causing much of a problem by generating significant heat. Even if the float draw was 5 amps, that's only an extra 2.5 watts. Then again, I'm not sure what happens when you exceed the float voltage on an AGM.

There's a lot of conflicting information. Many articles claim not to have an AGM battery in the engine compartment due to heat, but other articles state that an AGM battery handles heat better than a traditional lead acid battery.

[patrickt]

I thought I would update my battery experience since I posted on this thread earlier. For decades I have always been a proponent of Interstate batteries and that's all I've ever used in my ERA. Specifically, it was the Interstate Megatron II Group 47/H5 and originally it had a 75 month warranty and was generally good for seven years or more. That's a moderately big deal because changing the battery out in a late model ERA requires a bit of work while not dropping or losing the ten button head cap screws or rupturing your back wiggling the battery out of that wheel well. Specifically, you have to:

1) Remove the front passenger wheel and the four lower horizontal button head cap screws from the bottom of the wheel well access panel.

2) Remove the two lower shorter button head cap screws from the vertical side of the panel and a third longer cap screw at the very top.

3) From inside the engine bay, remove three more button head cap screws on the engine side of the access panel. Then ease the panel out towards the front of the car without ripping the the black ventilation duct tube.

4) Unbolt and remove the negative battery cut-off switch from the battery terminal. Disconnect the positive battery cable at the solenoid.

5) Remove the single hold down nut from the threaded tap. Years ago I added a threaded tap from underneath the tray as it made putting the clamp back on easier with just a nut.

6) Pull that 30 pound battery out through the wheel well with the positive cable still attached to it while not dropping it on your foot in the process.

7) Reverse the steps with the new battery.

It used to take me about an hour and a half to do the job. Then a little over two hours. This time we're going on three hours....

But the reason I'm posting this update is so you don't make the same mistake I did, which was not noticing that the Interstate MT battery that used to have a 75 month warranty now only had a 24 month warranty and ended up going completely dead in my garage after four years. Somewhere in the last ten years or so Interstate took what was the top of the line battery and downgraded it to where it was the lowest quality battery but kept the exact same name... and I never noticed (even though it is clearly printed on the battery). In 2012 I paid $125 for the super high-quality Interstate. In 2020 I paid $165 for the lowest quality.

So, I replaced it with an Interstate MTZ AGM battery... top of the line at $400, thank you very much for that screwing. At least it has a 48 month warranty, which should get me a safe five years. By that time, it'll probably take me six hours to do the replacement.

[twobjshelbys]

Almost all batteries are now made in a plant in Mexico and none of the manufacturers have the same warranty as before. Even the Optima's aren't much better than anything else. I left Interstate in my daily drivers and just went with the Walmart 3 year warranty version. The one in my Honda lasted 4 years. The one in my truck lasted 2yr-9mo and was replaced free with a new one that warranty is only the balance (3 months) but in practice will go the 3 years or so. Note sometimes Costco or Sams beats Walmart by a little bit and all are within 5 miles so I just get the cheapest.

[DanEC]

I had heard good things about Interstate and about 3 years ago jumped on the Interstate band wagon and put 27 series in my two 60s Plymouths. And almost immediately the feedback seemed to turn 180 degrees. So far mine are holding up OK but I need to make contingency plans for when they start to fail.

[cycleguy55]

Costco has been my 'go to' for automotive and lawn tractor batteries for many years now. I'm in Canada, and I'm told Costco Canada's battery supplier is probably different than Costco in the USA, but I've been happy so far.

BTW, my battery is in a sealed battery box in the trunk, in the big, fat, West Coast Cobra fender behind the right wheel well. It slides in sideways, so I use the side terminals on the biggest dual terminal battery that will fit. I can't remember the Group number, but can track it down and post it if someone's interested in that info. Right now it's a flooded battery, purchased in 2017, but I'll likely go with an AGM battery when it comes time to replace it.

[twobjshelbys]

Looking up Costco batteries on the web site redirects you to Interstate. Costco frustrates me because they don't list in-store prices and you can't see (like every other place on the planet) if a store has an item in stock. We only go for commodity stuff. We joined because they had good deals and selections on eyeglasses and still save money.