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Old 01-15-2017, 07:51 AM   #1
Lew
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The AGM Battery

My AGM Battery is on it's last leg I do believe. It's almost 5 years old. It cranks the car OK, but will not show 12.65 volts on my Multimeter. It only shows 11.8 volts no matter when it's checked. Just sitting with the engine off and the lights on with the radio on, it draws down the voltage quickly. My Deltran Battery Tender plus or my 6 AMP charger will not put a full charge on the Battery. I did a Parasitic Drain test recently with everything off, and it's fine showing only a 20 MA draw. Amazon has the AC Delco AMG which is a 48 series listing 760 CCA and 70 AH which is the series I have now for $155, and free shipping. With all my Amazon points I can get it for around 100 bucks. I might mention the things I hate are, NO VACANCY, a BUSY PHONE, NO ANSWER, and lastly a dead BATTERY.

I like having the AGM (absorbed glass mat) Battery, it's is a special design glass mat designed to wick the battery electrolyte between the battery plates. AGM Batteries contain only enough liquid to keep the mat wet with the electrolyte and if the battery is broken no free liquid is available to leak out. That's a good thing!

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Old 01-15-2017, 08:45 AM   #2
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I cheaped out yesterday and installed a new lead acid battery in my 2000S manual that was turning over kind of slow.
I went from the H6 size the the H8 used in tiptronic cars. The battery is larger but still fits fine. Car turns over very easily now.

BTW, Battery purchased was a Duracell branded battery from Sam's for $122.

I would have considered the AGM but my local Sam's was out of AGM in the H8 size.
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Old 01-15-2017, 09:46 AM   #3
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I recently put in an Autozone AGM battery, but honestly am not sure it'll be any better than my old lead acid Autozone Group 48, as that was already 8 yrs old when I took it out, and it was still fine. I doubt this AGM will last 8 yrs but am hopeful. I didn't want to throw in the larger Tip battery cause it's extra weight!
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Old 01-15-2017, 10:05 AM   #4
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2 suggestions so you do not waste your money on an unecessary battery replacement:
1. A tester that tells you S.O.H. and S.O.C.like this:
https://www.amazon.com/Autool-Bst-100-Battery-System-Tester/dp/B016OFE8FM
2. a desulphating battery charger like this
BatteryMINDer 1500 | 12 Volt Maintenance Charger Desulfator
The desulphating chargers will often rehabilitate a battery that shows only 50% S.O.H. but still take a full charge S.O.C.
If you have 'cooked' the battery by leaving it on an old trickle charger then it is too late.
To test for a frequent low battery problem ,search for "Parasitic Drain".Easy to test with a simple,inexpensive Multimeter.From a recent Post:
How to Find and Stop Car Battery Drains
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Old 01-15-2017, 11:10 AM   #5
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AGM is completely overrated.
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Old 01-15-2017, 12:27 PM   #6
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Except in some special situations?
"The leading advantages of AGM are a charge that is up to five times faster than the flooded version, and the ability to deep cycle. AGM offers a depth-of-discharge of 80 percent; the flooded, on the other hand, is specified at 50 percent DoD to attain the same cycle life. The negatives are slightly lower specific energy and higher manufacturing costs than the flooded."
Absorbent Glass Mat (AGM) Battery Information - Battery University
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Old 01-15-2017, 02:20 PM   #7
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Over rated?

If they are over rated, then why do OEMs invest in AGM batteries in their Auto Stop/Start versions of their cars?

If they didn't work better, they wouldn't spend the money to put them in those vehicles.

I bought this one:

NSB-AGM 94R/L4

I keep it alive with this:

CTEK Multi US 7002 - CTEK Battery ChargersCTEK Battery Chargers

Two years in, so far, so good. Car sits a lot.

Good luck.
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Old 01-15-2017, 02:57 PM   #8
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Originally Posted by 10/10ths View Post
If they are over rated, then why do OEMs invest in AGM batteries in their Auto Stop/Start versions of their cars?

If they didn't work better, they wouldn't spend the money to put them in those vehicles.

I bought this one:

NSB-AGM 94R/L4

I keep it alive with this:

CTEK Multi US 7002 - CTEK Battery ChargersCTEK Battery Chargers

Two years in, so far, so good. Car sits a lot.

Good luck.
Maybe it's just overkill for an older car without auto start/stop? I am only on my second battery in my 03 S, it is an Interstate that I put in in 2009 to replace the original battery. I use the older version of that CTEK - same as the one Porsche sold at dealerships but without the "Porsche" label and premium pricing. If I can get this long out of a traditional battery (OEM -6 years, Interstate - 7 years and still kicking), what's the benefit of AGM to me?

Now that I've said that, my Boxster has been out at the body shop for a week, and then goes back to my independent garage for installation of the sport suspension. With the car off the battery tender for that long, I may have just cursed my battery!
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Old 01-15-2017, 03:17 PM   #9
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Cursed ?
No
It is just chemistry. If the SOH is 50% or less but it still takes at least 90% charge, try to desulphating it. That is the specific problem that causes most lead+acid batteries to fail.
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Old 01-15-2017, 03:37 PM   #10
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Quote:
Originally Posted by Boxtaboy View Post
I recently put in an Autozone AGM battery, but honestly am not sure it'll be any better than my old lead acid Autozone Group 48, as that was already 8 yrs old when I took it out, and it was still fine. I doubt this AGM will last 8 yrs but am hopeful. I didn't want to throw in the larger Tip battery cause it's extra weight!
I know it's heavier, but so am I. I could stand to lose a hp myself.
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Old 01-15-2017, 03:41 PM   #11
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Quote:
Originally Posted by dghii View Post
I know it's heavier, but so am I. I could stand to lose a hp myself.
As can I!
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Old 01-15-2017, 03:47 PM   #12
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Quote:
Originally Posted by 10/10ths View Post
If they are over rated, then why do OEMs invest in AGM batteries in their Auto Stop/Start versions of their cars?

If they didn't work better, they wouldn't spend the money to put them in those vehicles.
The 986 is not a stop/start vehicle. It's also not a hybrid or electric vehicle. AGM is overrated and your statement is a prime example of that.
When was the last time you made an AGM battery? I worked for Johndon Controls for years, so take my word for it. They are a waste of money in most cars.
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Old 01-15-2017, 07:14 PM   #13
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Particlewave...

...I don't understand.

How was my post an example?
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Old 01-15-2017, 07:16 PM   #14
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not Your post.another one.
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Old 01-15-2017, 07:23 PM   #15
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Then why...

...was my post quoted?
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Old 01-15-2017, 07:36 PM   #16
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Also...

.....nevermind.
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Old 01-15-2017, 07:55 PM   #17
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Quote:
Originally Posted by particlewave View Post
The 986 is not a stop/start vehicle. It's also not a hybrid or electric vehicle. AGM is overrated and your statement is a prime example of that.
When was the last time you made an AGM battery? I worked for Johndon Controls for years, so take my word for it. They are a waste of money in most cars.
Well Particle I have a question then. Isn't a prime advantage of the AGM is that it doesn't outgas as much? Doesn't this help to prevent corrosion on terminals and lessen gasses in the enclosed frunk?
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Old 01-15-2017, 07:56 PM   #18
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That is why there is a vent hose on the car. Otherwise ,yes.
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Old 01-15-2017, 08:10 PM   #19
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Originally Posted by Gelbster View Post
That is why there is a vent hose on the car. Otherwise ,yes.
I understand and this is specific to the boxster, however the statement was that it is overkill for most cars. The lack of a vent and corrosion on terminals on most other cars makes this a highly valuable feature. I'm a fan of additional protection and don't like to see corroded terminals on any car I own.
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Old 01-15-2017, 08:24 PM   #20
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The frunk is sealed, but the battery is not in the sealed portion.

Vented batteries should always have their vent lines properly attached. Sealed batteries don't vent gasses. Corrosion should never be an issue.
AGM is overkill for these cars unless you get a good deal. Lead acid is more than adequate.
This is my opinion. Do as you may.

I have a deep personal hatred for AGM. We tried for almost 2 years to work out assembly issues, going home every single day itching like hell from the fiberglass. When I left JCI, these issues were still a daily thing. Take that into account when you read my hatred filled biased posts about them.


Last edited by particlewave; 01-15-2017 at 08:30 PM.
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