Battery ?
 

My 1974 911 will not crank at 11.56 volts. Every component will come on lights, headlights, fans, pumps with out dimming. Why is the simple act of turning the key an make the engine protest. New cables and terminals. Ground down neg. cable to frame for better contact. Thinking Optima Yellow as solution. The battery was bought in Nov.2015 at AA. Hair falling out as I type.Roger

11.56 volts is almost completely discharged! A full charge is 2.12 volts per cell or 12.7 volts for six fully charged cells. Put your battery on a good charger overnight. If you don't get up to at least 12.4 volts, or 80% of a full charge, with a load test, get a new battery. Don't forget to remove the surface charge by turning on the headlights for 30 seconds before you test. If you don't remove the surface charge you won't get reliable results.

Thank Dave. You instantly cleared the muddy water.Roger

Have you ever replaced the ground strap? The starter on my '88 would about 20% of the time not respond to turning the key. Would always start when I tried the key again. Thought it was the starter or ign switch going bad. Just for the heck of it I replaced the ground strap (underneath the car). Hasn't had a single hang up since! Starters require a good voltage flow. Solved my problem for less than $10. Of course, if the battery isn't producing in the first place, there's your problem; ground strap will help w/ delivery only, not produce more voltage for you.

Good info above and as stated, a typical reading would be in the 12.6-volt range when the battery is fully charged. If the reading is 12 volts or less, then the battery needs charging or needs to be replaced with a new one. Does the vehicle sit often? Short trips or the vehicle sitting will shorten the life of a battery and it might not be a bad idea to invest in a battery tender.

1974 Porsche 911 Base Coupe/Targa - Miscellaneous - Page 10

Engine ground strap replaced two months ago. Car does sit almost too much. The battery is a AutoCraft series 42 at 620 amps.. Would this battery be to small for application. Infamous #1458

Try a shock charge on the battery OUT of the car, you should get close to 13 volts. If not, replace it. Checking the ground strap is also good advice.

put battery on charger and reading 12.98 volts. Is this max for a battery out of the car? Thanks #1458

Is this with the charger on and connected? I usually get 13.5 +/- when charging. If this is the case I would say your battery may be unable to hold a good charge.

I have a Passat tdi that I rarely drive. Money pit! I have to put a new battery in it every year. Just eats them. Buy a trickle charger and keep it plugged in when you get a new battery and have it sitting.

Hello Everyone, Went out this morn to check battery voltage. The reading is 12.76 as of now. A .22 drop overnight. This battery is on a wooden deck with no chance of parasitic draw. Thoughts? Infamous #1458

Battery
 

Possibly shorted internally.

When the plates buckle or flake.

The battery should be tested for "cranking amp" draw.

Sears will do this at no cost to you.

Gerry

A normal battery will lose 1% of it's charge daily, give or take. Hook it up to a car that has a parasitic draw, as they all do, and it will lose more. If you're allowing your car to sit for periods of time without use, you can expect it to have a partially discharged battery the next time you get in it. Your best bet is too keep the battery on a small trickle charged when it's not in use and check both the battery voltage and electrolyte level somewhat frequently.

If you run your battery down too far too many times, you'll kill it.

JR

Day 2 of the 2 month old battery. This morning reading was 12.69. Me thinks continuing draw down maybe due to dead cell. The voltage draw down while battery is out of car and on wooden planks where no outside parasitic forces will give anything but a true voltage reading, Comments?

A battery will discharge slightly every day when connected to nothing. It can be sitting on a wooden plank, a cloud, or in a Playboy playmate's lap and it will do this.

It will do it faster if the outside of the battery case is dirty.

Your measurements are probably not entirely accurate, especially the first one you took after charging the battery.

If you have a dead cell, your readings would be much lower.

JR

Based on the info you've given there is nothing wrong with your battery. Around 12.6 is fully charged based on temperature.

The higher voltage readings after charging are probably due to surface charge where the chemical reaction takes place on the surface of the lead plates and will equalize out over time (or apply a brief load).

To be sure take it to Sears or to a FLAPS and have it tested.

I have a battery analyzer that I find invaluable. It tells you the condition of the battery internally. Mine is a HFT model that I have had for a couple of years and it has paid for itself many times. When a battery gets down to 50-60% I bring it back under warranty and they test it and give me a new one.

The tester electronically test the cranking amps of the battery, and also tests the internal resistance and gives you a % of capacity. I could not do without it.

This is the HFT one: Digital Automotive Battery Analyzer


I also notice Amazon has several of them on offer as well. I have no experience with any of these but they appear to be similar to what I have and the prices are very attractive:

https://www.amazon.com/s/ref=nb_sb_ss_c_1_11?url=search-alias%3Daps&field-keywords=battery+analyzer&sprefix=battery+ana%2Cap s%2C232&crid=36IUTJ28TY60J

One other point you haven't mentioned. Does it start the car after it was charged?