Dumb question but what battery size do the 1st gen SCs take officially? I see a group 34R (reversed polarity, positive on left rear...?) in there but I see about 1.5 inches of tray vacant. Whats the original group battery? I roughly measured 12x7x7.5 high from the tray dimensions. I m thinking I need a new one as the starter is really slow on a cold motor but starts up, sounds fine when warm started. A jump kicks it right over even when its cold. The status 'eye' is green which is a very basic hygrometer ball that floats up to the lens when its gravity is adequate. Will get it load tested eventually.

 

load tested and it was kinda OK...At 12.0V? Right out of the running SC that records 14.3V off the batt at idle, even with the lights on. Why only 12v? desulfating the battery with Epsom salt, worth a shot as the battery seems to be on its way out. BTW its only 2.1 years old, out of the 2 year warranty.

 

27F, I think? A charged battery should sit at 12.6+ volts with no load. At room temperature a good battery will stay at this voltage for months, no load of course.

 

I’m pretty sure it’s a 24F if I’m not mistaken. I change batteries in my SC pretty frequently and it’s the same battery my LS and ES use too.

I think there’s another size that can fit too from an old thread I read about a long time ago, but I never tried it myself.

 

Yep-- A 24F battery is one what the SC300/400/Soarer takes. I'm not sure if it's the original factory specified size but it works very well.

When using common a auto parts store search I also see 34R, 24F, 27F and "Size 35" listed. I think I used a 34R several years ago but at some point the 24F size just made more sense.

I highly recommend a battery rated higher than most auto supply stores will say this car "needs". A 700 CCA rating (Cold Cranking Amps) or higher is recommended.

The model I've been using for the last few years is an Interstate MTX (AGM chemistry) in the 24F type. It's rated at 710 CCA and 885 CA (Cranking Amps). Plenty of starting power in hot or very cold weather. Not a cheap model ($260 or so) but very worth it.

 

Attached is a spreadsheet I put together nearly 7 years ago, comparing the battery sizes that had potential for the SC. I highlighted the 27F as what appears to be the best option for max performance -- note that it is 1.8" longer than the 24F, which fits the OP premise -- but 24F as the typical replacement. I don't recall whether the 27F highlighting also meant it was the original spec... My notations are more vague on that point than I remembered.

 

I desulfated my low volt battery (750ml Epsom salt to 1.5l of distilled water into a drained and neutralized battery) and put it on the charger overnight at 10A, it pulled 8A for about 6 hours and finally leveled out this morning at about 10 am. I took it of the charger and let it sit for 2 hours. . Desulfate charge is supposed to be 36-48 hrs @ 2A. Started the car after 12 hours charge but it was very labored, barely kicked it over but it started on 2nd revolution. No load off the charger is only 12.9v after 12 hours, Idles it for 30 seconds turned it off and restarted, then it kicked over like a new battery! Is my starter contactor going? Never an issue when its warm, only when its cold, Lowest it gets here is 50F. Costco has thee cheapest new batteries around. A new Interstate green group 24 is only $99 plus a $15 core charge. Thats like 33% off Autozones new batteries.