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AGM batteries are capable of being charged at a faster rate, and may draw additional amperage from the alternator if it is not regulated. Many cars that come with AGM batteries have special charge rates (newer Porsche Cayennes that come with AGM batteries have a setting in the computer for this, for example).

I have an older Porsche Cayenne Twin Turbo that does not come with an AGM battery. Is it always safe to replace standard batteries with AGM variants?

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Yes for the most part an AGM is a drop in replacement for your standard Lead Acid Battery. The charging voltages are almost identical. You are correct that they have a lower internal resistance and can be charged at a much faster rate. This shouldn't cause a problem on the majority of vehicles as the wiring in the car is designed to handle the maximum rated output of the alternator.

  • Agreed - plug-n-play. Would also comment that if these batteries should ever be run down (ie: dead), they require a different type of charger to get them charged. Many newer battery chargers have an AGM setting on them, so should not be an issue. – Pᴀᴜʟsᴛᴇʀ2 Jan 12 '15 at 18:37
  • @Paulster2 Why if dead? Explain, not doubting just don't know – Move More Comments Link To Top Jan 12 '15 at 20:04
  • Optima is probably the most premier AGM battery on the market. They received a bad rap because people were having a hard time with them, stating they would die and then could not recharged. The main problem was that they were using the wrong type of charger, which did not charge them because of the battery state. The proper AGM charger will not only charge the battery from the deep cycle state, but will also not overcharge the battery, which can be bad for the AGM battery. Hopefully this helps ... if not, ask away. – Pᴀᴜʟsᴛᴇʀ2 Jan 12 '15 at 21:25
  • @Paulster2 The problem with charging Optima is not that the battery is AGM, it is that they use pure Lead plates. I am aware of one other company using pure Lead, Odyssey. Everyone else is using a Lead alloy, for AGM the alloy is Lead-Calcium. Lead-Calcium is even used in the majority of non-AGM battery types, with a minority using Lead-Antimony. The charging characteristics on all Lead alloy is relatively the same such that a charger that works on one will work on the other. – Paul Jan 12 '15 at 22:44
  • @Paul ... I didn't say it was a problem to charge them, it's that when you try to improperly charge them you have issues. Maybe semantics ... – Pᴀᴜʟsᴛᴇʀ2 Jan 12 '15 at 23:13
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I put a AGM battery in my audi a4 1999 , and the computer got confused enough to throw up annoying symbols on the dash , like bulb out errors and the like , so i changed back to excide premium 90AH , I recon the cars computer just could't figure out what had changed ,with the AGM being able to be recharged 5 times faster than the standard battery , but no damage done , every day is a school day .

  • I think your problem was related to something else. Perhaps your AGM battery was empty. They are often sold half charged! With either type of battery, system voltage is always between battery voltage and top charge voltage. It doesn't matter how fast battery can accept charge. – Evren Yurtesen Nov 21 '17 at 16:19
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I agree with Lee. I just put 2 AGM batteries in my 08 G8 Gt thinking it was going to be better and after some research it seems that older cars don't know how to deal with the AGM format when replaced being that the alternators aren't programmed to deal with AGM batteries. I started seeing high voltages when starting the car (15.6v) then after driving about 6 miles, the voltages would drop to 14.8v (normal for my car), then after 15 miles it would drop to 13.2v (definitely not normal). Got both batteries tested and they both show they're bad. I figure the initial charging of 15.6v (which I've never seen in my car before the install of this battery) is killing the unit. Going back to Autozone to switch back to a regular battery when I get off work.

With that said, let's not push everyone to install AGM batteries in their cars if the car wasn't designed to use it.

The following paragraph from this site helped me draw this conclusion:

https://www.knowyourparts.com/technical-resources/blog/three-misconceptions-agm-batteries/

"While the installation of the ­battery may be the same for the two battery styles, some vehicles require an extra step to tell the vehicle that the battery has been replaced. Newer vehicles have a Battery Sensor Module or similar systems. These systems require recalibration with a scan tool if the battery is replaced. If the system is not recalibrated, the alternator might overcharge the new battery and cause the battery to fail soon after replacement."

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