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I was under the impression that Optima did not make a battery that fit the 928. Is that incorrect?
Originally Posted by Jeff928S4
I used the "D35" Optima Yellow Top....
It is a tad tall, but if you place the tray that comes with it (that is supposed to go underneath to give it more height) on top, it protects the terminals from touching the battery compartment lid - and the lid holds the battery down.
Some have built lil' bars that attach to the bottom/front of the battery that will sit under the hold down lip in the bottom of the battery compartment.
It is also too short for the 928 battery compartment - I jammed cut portions of pool noodles down where there is space. That battery is not moving!
And that's the challenge...
Folks using these have discovered arc-welding damage to the battery cover, when the too-tall terminals-on-top battery that isn't secured vertically decides to get too close to the lid. It's possible to pin the battery down with a nice piece of urethane as an insulator, but you still have to wedge it in to keep it from sliding in the well. You could use a conventional universal hold-down if you don't mind drilling holes in the battery bucket to accept the J-bolts I guess.
Several places now offer the correct 48/H6 and 49/H8 sizes in AGM type, if you want to go that way. Just not the Optima "spiral-wound" AGM.
Cool that my smart battery charger/maintainer has separate charging and maintaining programs specifically for AGM batteries. Unfortunately my alternator doesn't. Lots of people use them anyway, and report success.
Another thing to look for these days is whether the new battery has the bottom lip along the short edge (end). The 928 uses this lip to "hook" into body for proper hold-down. Notice the photo of the Optima above does not have the requisite lip. I had a hard time finding a battery with the lip recently.
Just installed a Varta E38. Perfect fit. More than meets minimum 928 requirements with great CCA. Varta is standard issue in many European cars and particularly those in colder climates.
So, I went with the AutoCraft Platinum AGM Battery, Group Size H6, 760 CCA battery sold at Autozone because I needed a battery and it was available. (See first post this thread for a link.) The car starts better than it ever did, but I had to put some insulation over the posts in, because the battery mat makes the battery too tall. When done with my roadtrip, I will take everything apart and take the battery mat out. Then I will report back with some pictures on how the fit is.
I worked a discounted price (still expensive) on a NorthStar AGM in my 911 as a test case thinking it would deal well with the extended periods of non-driving. When it was new, I never heard that car turn over so fast. After a few months though, it slowed down to a more normal crank, then eventually crapped out. I couldn't find an amp drain (not much on that car to drain anyway), so I guess 3-4 weeks was too much to sit. I though that was below average for a fancy new battery. I recharged it and now it's on a tender just like the old Interstate (which was installed in 2001 BTW). It is back to cranking fast though.
Early '86 cars appear to use the larger longer size 49 batteries, but the late 86 cars (86.5, 86 1/2) use the same shorter battery as the 87s are listed as using.
I just bought an interstate MTP-48/H6 and it fits perfectly.
I tried to put in the MTP-49/H8 in earlier today but that was much too long and did not fit as well. So the change, like many other things, was during the end of the 86 build run.
My 1986 Porsche 928 Energizer battery size 49 purchased on 4/17/2004 finally died on election day 11/8/2016 that's over 12 years. I couldn't find a store carrying Energizers nearby so I want with a Pepboys Bosch battery for $123. My 928 is a weekend car and always connected to a battery tender.
Johnson Controls is an interesting company. I worked with a guy in Shanghai a few years back that worked for them. They make most all the batteries including Interstate Exide etc. They are all made under the same roof. They are made in China because it was easier for them to get away with polluting the ground water. My understanding is that Optima batteries don't have the cranking power that the average battery provides. At the Silver State they gave out Optimas to all the winners. No one including ourselves accepted them. They do look cool however.
My suggestion would to buy an O'Reilly battery. They are cheap but they work well for at least 3 to 4 years. On a long trip you can always find an O'Reilly store and exchange it for new one.
Cruising the local Costco, they now carry the Interstate H6 AGM for about $150. The standard lead-acid H6 is a little over $100, so I need to identify some extended-life benefit to justify the 40% upcharge for AGM in the 928. Thanks to the use pattern of the car, it will undoubtedly see the same maintainer use protocol that gives 5 - 7 years of useful life with a standard battery. Need to get out the calculator, but my seat-of-the-pants guess is that the AGM isn't the better choice financially.
I got caught by a maintainer last year. Common usage was to go out for a run, stop, one restart, go home. Then one day I did some short runs involving 3 restarts, then it died, nothing. A jump start got it home, and the battery charged up fine. MMMMMMMM.
Finally decided to test the alternator - ran it up at home with a meter across the hot post. After about 20 mins the voltage sagged down to 12.2V - alternator crapped out once fully hot. New alternator , 6 months later, battery still good and its now just over 5 years old.
So watch out for a maintainer masking a failing alternator, especially if your voltmeter is regarded as unreliable and ignored. There are cigarette lighter USB power outlets that also show volts - may not be accurate, but should be in the ball park re -is it in the 12s, or high 13s.
jp 83 Euro S AT 57k
07-14-2015, 09:04 PM
Lots of people use them anyway, and report success.
