ChuckD

I plan to get the smallest and lightest battery I can find for my 1982. I don't want to go nuts with a dry cell or racing battery. I just want a smaller one that fits in the compartment. So what are the electrical requirements that I will need for my stock car? Crankings amps, and whatever else??? If you have fitted a smaller battery (like a group 91 for example), let me know what has worked for you. Thanks!

mx22

Wouldn't the lightest battery shift weight balance towards the front of the car?

ChuckD

Yes, but I plan to remove the air pump. So...can you answer my question?

WallyP

There is no "answer".

One of the primary functions of the battery is to provide cranking power. My "answer" - the more the better.

If you use the car in cold weather, you will eventually need more than you have, since batteries get much less efficient when cold, and engines require much more starting power when cold. That isn't a good combination. I can't think of any trade-off that make it worth sitting alone in an icy parking lot with inadequate cranking power to get going.

If you plan to only drive on warm days, you don't need as much power. If you never drive at night, with AC and wipers on, you don't need as much reserve power.

This particular trade-off is very much a personal choice. The smallest standard battery will work - most of the time. The biggest standard battery will work more of the time.

Mrmerlin

the other issue you will have is the battery sliding in the tray,
since it will not be able to be securely fastened,
this can damage the ground wire and the positive cable.
and possibly lead to shorting of the terminals against the battery lid.
In this case more is better

fraggle

I'd hope the OP here would realize that an additional - lightweight - brace would be a requirement for a different sized battery. Technology in this respect has moved eons beyond what was available in 1982, and I really doubt that lifting a few pounds out of the back - especially if the air pump is also removed - will change the car's balance to the point that it would even be noticeable by most people.

As long as the replacement battery has matched cranking amp capacity with stock, I wouldn't worry about it. You could even cut some capacity in FL, as it isn't cold there.

Just remember to use a decent trickle charger, as should be done for ALL BATTERIES when the car is in storage.

MainePorsche

Get a battery that will securely fit in the 'box'. Be sure the contacts of the battery will not touch the compartment lid. Essentially get a unit with the most amp hours and cold cranking amperage that will fit.
Below is a link with a nice discussion about batteries.
https://rennlist.com/forums/928-foru...hlight=battery

dr bob

In addition to cranking/starting requirements, many find that the standard alternator and battery package does not provide adequate charging at idle in hot weather. If you spend time in traffic with AC running, and any combination of headlights, wipers, stereo, etc running on a hot day, the battery supplies power for those items plus fuel pump, injectors and ignition beyond whatever the alternator supplies at idle. More than a few owners have watched the system voltage dropping at hot idle. With a smaller battery, your survival time in that circumstance will be reduced. I hate getting stranded by stupid stuff like a car that can't even run its own fuel pump cuz the battery doesn't have the capacity. Plus, even if a small battery is barely up to the task now, a few deep discharge cycles will further reduce its ability to accept a full capacity charge again. Its a slippery slope.

What's the incentive for an undersized battery?

depami

^^^^^^^^^^^^^
Agree with all of that.

Unless you are a serious racer there is no point. Stick with the proper fit.

James Bailey

Just go on a diet yourself and you can drop thousands of dollars of weight off the car driver combination without touching the car ! Plus do you notice a big difference when the gas tank is full ?? there is 130 lbs or so there just in fuel. run 1/2 tank or less and drop 65 lbs !!! I often take students out on track in my car and having an extra 170-225 lbs makes almost no differences in lap times. And I have done many many timed laps. But if you must do get an Odessey or other such light weight battery also you can mount a mini 65 amp single wire alternator and drop a bunch of weight of the nose.

ChuckD

I appreciate the replies, gentlemen. WallyP-thanks for the thread on CCA and amp hours. That was the kind of stuff I was looking for. Still hoping to understand what the minimum CCA number that I need to start the car, drive it a bit and hear the radio. Maybe I will stumble upon it elsewhere or call a vendor and ask them what I need. Just trying to understand this particular car and its requirements. I have no history with any Porsches, so I beg your forgiveness while I learn. I have the manual, but on CD and it's hard to navigate all of the various folders on the CD. Thanks for all of your time on this topic.

jpitman2

I have found small batteries can be killed by a decent radio in a surprisingly few hours while you clean or work on a car...Running an 88Ah myself, cos it just fits.
jp 83 Euro S AT 54k

17prospective buyer

Stock alternator especially for later cars (87-) is inadequate. In my experience i had to rev my 928 to 3K at idle to charge the battery. To add to this most 928's have considerable parasitic current draw when "off".

James Bailey

Bull**** ! many of those stock cars have 150,000 200,000 or more miles. It is OK if the car discharges slightlty at idle with the A/C radio and lights on. Bigger is NOT always better. If you had to rev the engine most likely the exciter circuit (light) is faulty and you need the RPM to kick start the charging.

SeanR

OP, what are you trying to accomplish with a smaller battery?