rw229

I have an old Interstate Yellow Top that's ready for replacement. I've called Optima to see what their equivalent is and they can't cross reference the Interstate numbers. As near as I can tell by measuring and the terminals, it's a D34/78.

Searching here, it seems most have installed the D35. Is there and reason I should go with a D35 over a D34? (I obviously don't need the /78 side terminals) Is the D35 bolt in or do I need to modify the hold down?

JM993

D35 works and fits perfectly.

S98CS

I just use a optima red top
this unit is not as heavy not as heavy
SC

97_993C2

I may be remembering incorrectly, but I thought the difference between the 34 and 35, at least in the red top, was the positive and negative terminals were switched - the batteries were the same size???

My bad. I checked the website and the D34 is slightly larger. I also looked at my installed red top battery, and it is a 75/25 installed backwards so the cables would reach the correct terminals. IIRC I was looking for a D35 at the time because it has the lip on the bottom and right terminal orientation, but could only find the 75/25 that is close to the size of the D35, has the bottom lip, and fits.

pcarrera993

I just put D35 in my car, fits perfect.

Mike J

Drop the Optima, they are crap batteries. When through a few, gave up and went back to the old fashioned reliable lead-acid batteries. The Optima's just seem to fail.

I would not go back to them.

Do a search, there are some threads around as well discussing the "merits". Several people have had issues with short life and failures.

Cheers,

Mike

Ed Hughes

There are also positive reports of Optimas. I've never had an issue.

JM993

The Yellow Top Optimas are a different animal than the Red Top Optimas. Love mine and, being a deep cell, it really makes sense for weekend/non-dd cars.

rw229

Well... My current Interstate branded Optima Yellow Top battery is from 2001 and is just now becoming unreliable. I think 10 years is a pretty darn good life for a battery. The unknown is the current quality of the the Optimas. Mine was made in Colorado and the new ones are manufactured in Mexico.

So with a little more research, I've determined that both the D34 and D35 will work, but still not sure which to choose.

D34
750 CCA
42.9 lbs

D35
620 CCA
36.4 lbs

I'll probably just go with the D34 as it the same as the current is a D34/78 unless someone has a good reason not to. I do track the car, but only DE and the 6.5 lbs probably doesn't make a difference.

cosmic_993

D35 yellow top is my pick and in my car...

Mike J

Mine was yellow top and as I said, never again. Best of luck!

Cheers,

Mike

pdemar

Yesterday installed a yellow top D35 since it's not driven frequently - perfect fit.

97_993C2

I've read most of the threads about Optima batteries on RL and my personal conclusions are they are very good batteries IF they are not allowed to discharge too much. If they are, then their life will be DRASTICALLY reduced. That is why I maintain mine on a trickle charger whenever my Porsche is in the garage.

I have a red-top in my mostly weekend driver 993 and have been very happy with Optima, but it is only 30 months old so far. A big reason why I decided to try an Optima is the fear, no matter how remote, of possible battery acid spills. I had burn holes in the trunk carpet of my old '74 911 from battery acid.

Ed Hughes

Carpet is nothing. It is the number of 911's showing corrosion in the cross-member below the battery which is alarming, and wayward acid is the culprit. Since this is the front support for the torsion bar, it is not a simple fix.

abiazis

From what I gather, if the car has lots of electronic accessories and sits a fair amount of time - go with Yellow..

If DD, go with Red top?

Thanks for any info or opinions on this......