^^^ And if they go completely discharged....chances are they won't re-charge.

The ability to tip over without leaking is not a big enough plus for me. If I end up 'tires up'...I'm not concerned about my battery.

I've completely discharged my Optimas several times. They've all come back to life just fine - though I did have trouble with an aforementioned semi-smart charger once that failed to recognize the battery.
YMMV of course... whatever works for you.

From their own website:

Good info Graham...thanks.

(edit) Steve, for years the early twin batteries 911 was plagued with rusted out battery boxes. Actiallu they were eaten out with battery acid. Sloshed out when cornering hard at autocrosses and track days. Keeping the acid level low, just covering the plates, helped. I kept mine good by frequently pulling batteries and cleaning the boxes with baking soda/water mix. then more cleaning...

Nevertheless, when spill proof AGM batteries arrived, I welcomed them with open arms.

I used to use Interstate for years on my boat. I have a 2 battery setup with a Perko selector switch. It's only a 19' boat with a 150HP outboard, but having battery issues on a boat is not something I want to chance.

My Interstate dealer closed his shop - retired. So now I'm going with another brand from my FLAPS. A Super Start Marine battery - conventional. About $100 each, so not too bad. Some of those fancy batteries can really cost some big bucks!

^ I had a great experience with a Super Start battery in my tractor, until someone stole it. Now I'm stuck using the Insterstate one for a while.

Good reviews so I'm all in.....

Yep. My first and only one that lasted over 10 years. It came out of a cop car my friend's father gave me. He was a mechanic as a local city yard. They swap them out every two years. This was way back around early 2000s. No spill was best I liked about these batteries. All the ones I bought later would die just under 2 years, Red top seem to last a tiny bit longer then 2 years, but all my yellow tops were like clock work, dies right at about 2 years, in my daily drivers or 911 that are on battery tenders. Will not buy them again.

AGM need a smart charger. 20% of the Amp-hr rating in Amps until the battery reaches 14.4V. Then constant 14.4V with diminishing current until current is near 0. Then drop voltage to ~13.8V and hold.

I'll post a diagram tomorrow.

I have 10 years old 12V AGM battery in my Chevy Volt. Still fine. It is not used for cranking though.

I'm getting this one DieHard Platinum AGM Battery, Group Size H8, 900 CCA

Should work well. Report back in a few years & let us know? Any idea who/where the new "die hard" batteries are made?

[QUOTE=dad911;11573928]The 'computerized' fancy charger didn't think a battery was connected. The 40 YO sears charger is supposedly charging it.[/QUOTE

I've had this happen as well.

Looking at new batteries and was searching here for input.

Did you ever install this?

I have an 86' Coupe and am pulling the boat anchor Interstate Group 49/H8 out of it. Going with a Group 48/H6 and AGM.

Thanks for your time!
Erik

I have a schumaker 'smart charger' that came with the most basic instructions (how to hook it up, no explanation of any settings). I didn't trust it so used my voltmeter to graph what it actually does. Turns out what it does is mostly as perfect as my understanding allows. I wish they'd described the heuristics and given me graphs but now I'm happy with it. With fully discharged battery I've been able to bootstrap at autodetected 6v, then unplug and it will continue with battery as 12v. Key is it has a 'force charge' button. I think its surprisingly sophisticated and well designed but I couldn't appreciate it until I mapped its behavior with a multimeter. Is a case where product is pretty great but instructions keep everything mysterious.

I'm asking next bit because I want to understand.

How can a charger apply 14.4v to a battery "with diminishing current"? If voltage is constant isn't the amount current up to whatever the battery accepts? Can't control them both.

Translating what you wrote to voltage control:
To charge AGM:
1) maintain voltage to battery so that current is 20% of battery's ah rating - until voltage reaches 14.4v.
2) Maintain 14.4v until current drops to nothing.
3) Maintain at 13.8v (which really means no current until battery's internal false voltage drops to 13.8v)

Yes?

I think what red-beard meant was that the charger voltage and amperage is altered by the "smart" charger designed for AGM. "current" used to describe amperage. In other words, voltage begins being delivered at a higher amperage rate than it ends with.

Erik, I did get it and it's been a good battery.

Thank you sir!

Erik

Speaking of batteries, and moreso about analog vs. digital cars, my 84 Carrera has been sitting for 2 months. High 40s today and nice sunny day so I thought I would take it for a spin.

Started right up like I've been driving all summer.

I bet the Cayenne has a 3 week battery lifespan if not driven.

Yep..even with everything off, the new cars eat electricity. Too bad they don't give owners an idea of the amperage draw.

On my old 911, the battery (a Diehard if I remember correctly) lasted something like 15 years and I never used a battery maintainer. There's something to be said for the oxcart simplicity of that car.