dr bob

Cars with the dual pipes running to the rear need the room between the battery box and the diff cover to get that pipe over to the rear muffler. So the shorter battery is needed too. The older cars with Group 49 share with Mercedes diesel models and other high starting demand cars, by the way.

davek9

Exactly, the "shorter" battery boxes started in the 86.5 model 32v, when they went to a full dual exhaust (no shared resonator). Stayed that way with the S4's and through the rest of production from what I've seen.
MY's 85 and 86 32v still had the "longer" battery box, and so do the 16v ers.

edit: you may also want to consider an AGM battery, no liquid, fiberglass mat soaked in acid gel, have standard size one, not an Optima, in the 86.5 (gold car) works and fits great.

Fnic99

Thanks for the help everyone. I brought the 48 back to the store a few days ago so can't take pictures. No insulation on lid or bottom of the box. I will buy another this week and try again.

Fnic99

BTW - I have been driving the car for the last 2 years with the 40R. Always started fine. What are the negative aspects of using a smaller battery?

davek9

the physical size doesn't matter, its the cold cranking amps that does.

Alan

With a smaller battery how do you secure it to the box?

Smaller likely means less CCA and less RC (Reserve Capacity).

CCA gets you strong cold starts, RC gets you home when the alternator packs it in - more of both is better. An unsecured battery is very bad news...


Alan

F4GIB

This one fits fine in my GTS.

dr bob

I think I tested the capacity of the battery some in stop-and-go L.A. traffic, 90º+ and AC cranking. Even with a good alternator and new cabling it wasn't keeping up with running load in the car, so it was running on the battery some to make up the difference. In that situation, total AH capacity became the center of focus.

The difference in cost between a 40R and the 48/H6 is virtually none, so I can't see any justification for using less than the original spec. The original hold-down is very secure with the group 48 too, so no need to come up with any alternatives for a smaller case. And no, stuffing the area around the battery with used baby diapers is not, in my opinion, an acceptable workaround.

Fnic99

Thanks for the help everyone. I need to buy another 48 battery this week but I have getting home from work very late.

Dr. Bob - thanks for the info. Not considering a 40R again but wanted to know if it this could be causing the car to idle a little rough. I am eager to see if the idle improves with a new battery.

dr bob

That dash voltmeter has to be good for something... Was/is the reading noticeably lower when the rough idle reared its head?

sstrickstein

As was said it more depends on the store and the warranty. I live in Phoenix. No matter the battery you don't get much more than 24 months here. The heat kills batteries. So buy with your climate in mind. I replaced mine at orielly last year and so far no issues. Big damn battery. 1000 cold cranking amps is a lot!

SwedeInSiam

Add the humidity to the heat like here in Thailand and you only get 12 months out of any battery.
And when they go they GO, car just stops in the middle of the road

Fnic99

If I remember correctly, it only happened when I was idling with the AC on. The entire dash would get dim and the tach would drop below 500.

dr bob

Fnic99 --

The most significant benefit on that front came from replacing the ground strap, believe it or not. There's a thread in here someplace on my efforts to maintain system voltage, and those include replacement of primary cables, alternator, and more. We found some 2ga tinned-copper ground straps, added a shrink sleeve, and suddenly full charging current was again available to the battery. That in turn meant that there was enough battery capacity available to safely cover the idle case when the alternator didn't put out enough current to cover all the electrical loads. Our major suppliers (928 International, 928srus, etc) carry the heavier-duty replacement straps for a very reasonable cost. A fringe benefit to having full current available for charging is that the bettery is less likely to be drawn down so far that there's risk of damage. Get down below 11 volts, and you are eating seriously into the remaining life of the battery. I was getting down into the two-three yaers of life range on batteries, and blamed it on the batteries; turns out it was probably the car eating them.

And-- put new bearings in the cooling fan motors.

Steen Jensen

I had this problem years ago. The door would not close. Upon close inspection , it turned out the battery box had been pushed up. It was not obvious.