I forgot that Interstate does this too. Batteries that sat on the shelf longer than whatever the determined time frame is are sold at a substantial discount and a 6 month warranty.

 

There is a Deka dealer not far from me. I'm going to check it out. As far as I can tell they are less expensive that the run of the mill batteries that we know are crap.

 

The only lead batteries I have found that will really last are the Enersys/Hawker series batteries. Yes they are AGM but their construction is good. I have had ones that were sitting dead for 10 years come back to 90+% capacity.

Reason: Pure lead, good plates, very high quality interconnects. Just don't overcharge them.

 

Our local Costco is carrying Interstate batteries for about $100 last I looked. A bargain. Put one in my DD a year or more ago with no issues so far.

After dancing with Autozone a few times on their Duralast Gold batteries under warranty, I ended up putting a Walmart battery in the 928. The car also received some cable upgrades that didn't improve charging, at least not until the ground strap was replaced. The replacement is a 2ga tinned copper braid strap, with a plastic shrink sleeve added to protect it on the way from the negative terminal to the rear apron bolt. That single change made a huge difference in charging and ultimately in battery life. That same Walmart battery is now over 7 years old. It showed some weak cells last spring when I tested the specific gravity of the electrolyte, a situation that has been remedied using the 'recover' feature in my smart charge/maintainer.

I typically depend on five years of useful life from vehicle batteries, and plan to replace the 928 battery in the spring when the car comes out of hibernation. Know that the parasitic drain on my car is low (about 35mA last I looked) and it sits on a maintainer during driving our seven-month season when left for more than a week, and has a CTEK US7002 smart maintainer connected to the disconnected battery during hibernation months. The difference is how often the maintainer cycles in use.

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Since you have the GB alternator installed, you likely have the requisite cabling and ground strap upgrades already installed in your car. If not, you'll want to do those upgrades to take advantage of the increased alternator capacity. Voltage drop in the charging and primary supply cabling are directly related to the system's ability to charge the battery and allow the alternator to carry more load directly. I know there was an engine fire so will also assume that the front harnesses in the car had similar primary power cabling upgrades.

 

My 2 cents worth here,from a professional auto tech,involved with up to date new car technology.Take it any way you want.Caution...YMMV.

Johnson controls is "Interstate Battery"
Johnson controls also supplies the Walmart Everstart series and,last time I looked, the value priced series they carry,the name of which I don't remember as it has just chaged.GREAT batteries for $49.95 as far as I am concerned.No,I don't put them in my 928.
AGM batteries are fantastic.I have been using them for over 20 years now,again,not in my 928.But in my my 2 chevy trucks,10+ years under the hood with no issues.Dual batteries in my 6.5 diesel Suburban,single unit in my C2500HD P/U.I even use one in my Suzuki Samurai thats a clone to the starting battery in my motorhome in case I need a battery for it when out on camping trips. Had a new vehicle take out in my jag for 11 years before selling the car,with the same battery,that still read out 95% battery life left with 950CCA after 100K miles of service.
Our current new vehicles that I am involved with have AGM batteries from the factory since 2016.Excellent CCA at over 900 amps,great reserve for hi demand accessories.Hell,these vehicle pull 75 amps when you just turn on the car without starting it.
YES,AGM's are a royal pain in the butt to charge.At the shop,we have a "pulse" style charger that the vehicle manufacture requires us to use for all battery related issues,with a print out when done.
YES,AGM's can fully recover after being fully discharged to "0" volts.YES.it is another pain in the butt.
The battery mentioned above in the jag was a dead,zero volt take out from a 5 mile new vehicle that was sitting in the showroom. After swapping out the battery and firing up the vehicle that a customer wanted to test drive,I sat the take out on a trickle charger for 2 weeks to bring the static voltage up to 8 volts,then charged it on a regular hi quality battery charger at 2 amps for about a week.That brought it up to 12.7 votls static charge and 900+ CCA.Put it in my car and never worried about it.AGM's can not just be forced charged.Don't work.Not at all.Just burns them up by pin holing the insulation between the layers of the mat structure..Result,a battery that never regains it CCA and a battery that now wants to self discharge.
I personally have found that both the 928's I own are slightly hard on batteries,with usually getting about 4 to 5 years of service out of the highest output interstates that I can buy for them.Sometimes I wonder if its the location,as that compartment gets really hot from the exhaust that is just not that far away.

 

What about weight for an AGM? The 2-6v AGM's I have weigh 90#'s each and they are huge. I paid about $375 each ( Lifeline)

About 10 years ago I worked with a Chinese guy in Shanghai ( we were making garage stools) and his last job was for Johnson Controls. He told me that the reason they were made in China was because JC could pollute rivers and streams without complications and they had multiple brands all in the same factory.

 

I know the Bosch AGM was the worst battery I've tried in my car. Very expensive and only lasted a little over a year. The current Die Hard is going on 3 years. The AC Delco lasted 2 years as did the one I got from Napa Auto Parts. The Duralast from Autozone did well for a couple years, then seemed to discharge quickly, but didn't die, so I keep it as a back up. When I first got the 928, 20 years ago, I used Interstate batteries. They'd last 3-5 years, but the last one I got only lasted a couple so I started trying other brands. I still haven't found the perfect battery...

Here's a battery comparison on Youtube:


__________________
George
90 S4 Grand Prix White (Murf #5 - 219.0 mph top speed)
94 GTS 5-Speed Midnight Blue
06 Cayenne S Havanna/Sand Beige (PASM)
http://928.jorj7.com

 

It may be superstition at this point, but I have gotten 6+ years out of every Autocraft "Silver" Group 49/H8 I have had, so I have stuck with Advance Auto Parts for 928 batteries.

 

I have had great luck with Napa Gold batteries. Last one I bought for my 81 lasted 6+ years until the head gaskets went. It was $120 at the time.

Haven't had good luck with champion. My dad's 944 eats those for breakfast.

 

Don't be afraid to test the specific gravity of the fluid in the cells to see if the battery is actually getting a full charge. That was the telltale when I was chasing down battery and alternator/charging problems. For new batteries, charge them with a smart charger before you install them. Grab a baseline gravity measurement on the fully-charged battery if you can. Goes to logbook. After that, lower gravity readings will tell you when the battery isn't getting a full charge when driving. A maintainer will mask some of that, so take readings an hour after driving, If the numbers are lower, find out why the battery doesn't charge completely.

The comment about 'if it will start the car, charging doesn't hurt the electrical system' may be misleading. A battery that's tired and will no longer take a full charge may be able to start the car, but the higher recovery-from-starting demand and the higher continuous-charging demands from the battery, both on top of the normal power demand from the car while driving, will kill an alternator. The alternator rating is typically at some RPM and temperature that are seldom seen in actual service. Engine speeds vary a lot, and in automatic cars are seldom maintained at spec levels for the alternator. Engine heat plus alternator load quickly take internal temps above the guaranteed-performance temperature. Adding load for excess charging needs only makes the problem worse. Got accessories? Worse.

GB's alternator solves the load issues, masks some of the voltage drop issues, and with new upgraded primary wiring will solve charging and related battery-life issues.

 

The last time I drove my car it was near dark, cold and raining. I had the headlights on (H4) + fog lamps, heater/fan wipers and of course the radio. It stalled a few times at intersections. I'm now wondering if the battery was going soft then and it was not producing enough amps to keep everything going. Put the car away and now the battery is dead. My amp meeter has never been on top of things so I don't fret over what its reading
Just think the new Audis' have a 48v system

 

After good luck with a 2002 era Interstate Battery lasting for 15 years (longer than any other battery I ever had), I began to swap over all batteries to Interstate brand. Have yet to take one back or buy another for each vehicle.

I understand on the fact they are all made by a narrow group of manufacturers. That's fine. Interstate must have better QC than parts stores, or they rotate their shelf stock enough, I never got one which "sat". YMMV

 

Although that sounds reasonable you haven't convinced me--yet. Not all, but many batteries--in millions of cars--'get tired'. If what you say is true, I'd think we'd see a huge number of alternator failures along with those batteries, and I can't say that's something I've ever seen /heard. Not saying it doesn't happen at times, but I don't think it's common.

The other point I'd make is the fallacy of saying "My battery made by X went bad in two years, so they all must be junk." It's a valid anecdote, but not a reasonable statistical point, by itself. What you are NOT hearing about is all the batteries made by X that did just fine for 5-10 years. If a significant number of ANY manufacturers' batteries went bad in, say, 1-2 years, you'd likely hear the hue and cry about it, and they'd likely be worried about staying in business.

And last, if you've got batteries going bad, frequently, in less than 5 years, I'd agree the car charging system needs looking into in the way Dr. Bob explained.

 

That is one of my all time favorite YouTube channels.

 

For a long time I was happy going down a path that included battery replacement driven by the "no longer starts the car" symptom. Autozone swallowed several batteries from the 928 that had "failed" to this symptom at well under the seven year warranty period. I and they were both getting tired with this. The meters (DMM's not the dash gauge) showed that the alternator was doing fine, so the charging 'problem' had to be the batteries. The telling symptom though came with the fact that the car started fine at the home garage after sitting on the maintainer. I was using the car as a DD in SoCal, and the hot weather, AC, fans, etc caused me to get to a slow-crank condition by later in the week. I drove around with meters and test leads strung into the cabin from test points in and under the car. What was keeping the battery from taking a charge? New alternator, new primary battery cable, both replaced even though the meters showed they were working fine. The collective here said to replace the ground strap, but the meters showed it was working fine, plus it looked fine on visual inspection. Finally replaced it anyway because it was the last possible link in the charging path. Suddenly the battery was accepting a full charge again. But... the battery had suffered from the lack of proper charging and multiple cycles. My 2.5 amp maintainer was maxed out even while the battery was disconnected from the car, another telltale. The alternator came with a warning that the battery needed to be replaced at the same time or the warranty was void. Two years into the life of the battery, Autozone balked at the warranty replacement. The charging current and alternator load (amps) remained pretty high with engine running cold (no fans lights AC etc), suggesting that the battery was not doing its job well. Testing specific gravity regularly told me that it wasn't ever reaching a full charge, even with the proper terminal voltage showing and the high charging current. So I stepped sideways out of the Autozone battery warranty trap, into a Walmart battery that was in all ways identical to the Autozone it replaced. Put it on the charger maintainer overnight before connecting it, even though the spg test showed it was very close to full charge from the shelf. Charge current from the alternator to the battery dropped by no less than 10 amps in that cold run testing.The Walmart battery has been in the car for over seven years now, and is finally telling me by spg readings that it's due for replacement. No need to abuse the alternator, trying to charge a battery that is no longer willing to charge completely.

So: I think I hit on the 'batteries made by X going bad in less than two years'. The resistance in the failing ground strap "saved" the alternator from the high charging current needed to recover the battery charge capacity. Once that was fixed though, the 'tired' battery was drawing so much current that the battery terminal voltage was still not reaching alternator-rated 14+. Specific Gravity in the cells was a telltale, and that testing is now on the Annual Electrical Maintenance schedule each spring, part of the un-hibernation protocol. All that $hundreds fuss over a <$20 ground strap. I replaced bearings and brushes in the original alternator, and it's good as new in the "working original spares" bin that goes with the car.