Replace battery by specs & size only?

[FlaCarrera]

Quandry is PO put in a monster battery. I want to replace with a top brand (Die Hard, Optima, Interstate) BUT smaller in physical size than what sits there now. The battery in my SUV is about 65% the size of the one which lives up front in the P car. I plan to buy a 700-800 Cold Cranking Amp rated battery (Die Hard web site says 650 min. recommended fo 86 911).

In other words, buy soley by 1) capacity & CCA specs AND 2) smallish size. Gotta get that monster outa there. I think this logic works or am I missng something? Cold weather not a factor.
Thanks
Ted in So Fla
86 Carrera Targa Blk/Blk

[bell]

stick with the same rating or bigger when it comes to specs.
alot of people like to run the optima batteries but they are a capacatance type battery which puts a heavier load on the charging system, lead acid batteries although "old school" will have better longevity than a "dry" battery. i can't tell you how many optima batteries i've replaced along with alternators they have killed.
i can get into this more if you want to hear

[A Quiet Boom]

I'll second bell's problems with Optima batteries. I've had the same problems and not just with P-cars but also my truck with a heavy duty alternator and my racecar which has dual batteries. In both cases my alternator died early and so did the batteries, now my truck has had the same 1000CCA Interstate battery for 4 years without incident. Even in the dead of winter it starts my 460 like it's a fourbanger.

[FlaCarrera]

As usual great tips here. Optima off the list Search continues for lead acid type with ample CCA & reserve rating but smaller overall dimensions. A brand search using similar HP import cars has revealed some good (smaller sized) choices.

Cheers from So. Fla
Ted
86 Carrera Blk/Blk
Euro pre-muff & Dansk twin out tommorrow

[ccandgc]

Thanks for saving me from that problem!


ChadC
71 911S Targa

[FlaCarrera]

Quandry has been solved. Bought a smaller Interstate with 1000 CA and 800 CCA,... quite a bit smaller and lighter than the beomouth that was there. Interstate calls for a (physcially) larger one than I bought, but figure this has all the heft required. Besides, it contributes another 9 lbs to the weight reduction of happening today with SS muffler & cat by pass.

Cheers
Ted in So. Fla
86 Carrera Targe Blk/Blk on a weight diet today

[steve911]

Ted--
Could you share what brands/models you came up with in your search? Would be very helpful for when the battery dies.....

[911pcars]

"..alot of people like to run the optima batteries but they are a capacatance type battery which puts a heavier load on the charging system, lead acid batteries although "old school" will have better longevity than a "dry" battery. i can't tell you how many optima batteries i've replaced along with alternators they have killed.

i can get into this more if you want to hear "

Yes, I'd like to know. Please provide more info.

Thanks,
Sherwood Lee
http://members.rennlist.org/911pcars

[bell]

i left all my technical notes at work so i don't have the equasions in front of me......
basically starting with the alternator, when an alternator spins, the windings on the shaft work with magnets around them to create an a/c electrical charge, this charge then travels through diodes to turn the voltage into d/c current. an alternator dies when the diodes burn out from too much current which is turned into excessive heat. the alternator works reguardless of the regulator as long as these diodes are working properly, the regulator regulates the excessive current by turning it into heat (the extra voltage needs to go somewhere).
when a regulator fails to disipate the heat all the extra "unregulated" voltage then travels through though the electrical system and to the battery.
this part is important.......
the battery is a load which is needed for the alternator/regulator so it can smooth out the voltage/current ripples.
these ripples can be seen at a low idle with a weak battery by the lights flickering.
so if you have a battery which is either deep cycle or has a high capacitance (they are related) it makes the alternator/regulator work harder because the of the needed current to keep it charged due to the higher rate of discharge.
these batteries work well where you need high current for long durations at a time (not just to starting the vehicle) like with high powered audio systems or multiple high output lamps (rally lights).
when you don't need the excess current you're simply overworking the alternator/regulator which will shorten their life considerably.

lead acid batteries are a more stable platform because of their slow charging/discharging rate which stablizes the charging system, which is what they were designed for.

another fact is that car electrical systems work in reverse of the way most people think. although our cars are a negative ground the current/voltage flows from the chassis then through the electrical system, in the early 1900's auto manufacturers found out that by using the chassis as the primary source of power they could eliminate alot of the costs in driving electrical components throught the vehicles by having to have double the amount of wiring.
this is also why ground wires are SO important since they actually supply the needed power to operate everything properly.
but this topic can take days to explain, i'm going to get together some documentation to show how this is and i'll post it here in the next couple of days.

hope this all made sense, i had a long day

[ccandgc]

Thanks!

ChadC

[TimT]

try this if you want to lose some bateery weight

[TimT]

battery

[bell]

Originally posted by TimT
try this if you want to lose some battery weight

they say it works great "with one of their alternators" but i doubt you would be able to adapt one to your 911

[FlaCarrera]

What I ended up with is the Interstate MTP-24 with following:
List Price 98.95
Suggested price 81.95
Weight 50 Lbs.
11" L X 6.88 W X 8.75 H
Cranking Amps 1000
Cold Cranking Amps 800
It's 3.38" shorter lengthwise than the MTP-93 Interstate suggested for Porsche 911. but 1.87" taller. Fore >aft room was what I was missing with the brute the PO put in. There are even smaller ones with a little less CCA ratings on the Interstate Batteries browsing site;
www.ibsa.com/estore/browse_category.asp
(Sorry can't seem to paste a link.)

I did a non-scientific, random shopping search for passenger cars with similar engine displacement and found the MTP-24 showing up again and again across a broad variety of model lines. Hope this helps.
Cheers
Ted in So Fla
86 Carrera Blk/Blk

[deltajetfixer]

Originally posted by bell
as long as these diodes are working properly, the regulator regulates the excessive current by turning it into heat (the extra voltage needs to go somewhere).
.

Uhhhh...I don't think a voltage regulator works like a rheostat.

Ones I'm used to vary the field (rotor) strength. A temperature sensing element present in the regulator will allow more charging current at low ambient temperatures.

No "extra voltage" to worry about "going anywhere" as it's not produced in the first place...

[Early_S_Man]

bell,

Delta is correct ... so before you publish your next treatise, throw away your old 'technical notes and equasions,' and read up in the Bosch Automotive Handbook section on electrical systems!

[nhromyak]

Interesting... I have had my Optima for three years now.

No problems.

[Axeman]

Well I just put an Optima in mine..hope I don't have any problems..or at least not for a couple of years!!

--Michael

[6 Shooter]

I put an Optima in my 914-6 around 1993 or '94. On the way home from the'98 Monterey Historics, a rock lunched my windshield (covered by comprehensive insurance, zero deduct). I parked the car for 2 1/2 years, didn't start it, never opened the door, never charged the batt., didn't disconnect the battery. Around March/April 2001, I finally made arrangements to repair the windshield, opened the door and saw the dome light working. I had planned on recharging the battery, hoping that it might hold a charge, but was curious (I had expected a dead battery) and load tested it. I didn't use a VAT with a carbon pile to load test it, just a hand held tester (Snap-On) with a set resistance. I depressed the button for 20-25 seconds until the tested was glowing orange and hot, the voltage was still 10.4 volts. Minimum should be 9.6V after 15 seconds. My car still has an analog radio (no LED/LC display or memory drain) and no clock.
I bought another Optima (in 2001) for my early S, and two more (in 2000, 2001) non P-cars. I'm happy with my Optima batts, hope that I don't have bell's/a quiet boom's problems. Fingers, crossed.

[TimT]

ive had the dyna-batt in my car for 2 yrs now... it works fine, I dont know if it would be good for a car with alot of currrent draws, i.e a/c, power windows, an ECU, a radio with memory.

that battery works finein a striped down bare race car that I have