Need input about battery voltage?

i just installed a new Battery , off the shelf measured 12.95 volts , and it had been setting around a month!
put it in , and fired up instantly, engine turned over faster , much impressed, gages read quicker etc.
so went out for drive , everything fine!
measured 13.5 volts idling, shut her down for the night , next morning measured 12.7 volts with cable off, turned over slower, but did start OK!
if i put small 2 amp charge on it , all things react BETTER!
QUESTION for Gurus, how can i keep the cold voltage, like maybe .3 tenths volts MORE?
at 12.9 everything acts better, it loves 13 volts!
do they make a 13volt battery ? anybody?

Back in the day of 6V cars, somebody made an 8V battery. I think you’re outta luck on the 13V, though.

0.3V shouldn’t make that much difference to starting, though. It might make a noticeable difference to headlight brightness and whiteness, that’s about it. You’re probably seeing some unrelated effects.

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I believe battery voltage at 12.6 volts would be considered normal.
You should check for any parasitic battery draw. Plenty of you tube video’s on the subject.

For overnight I use my battery isolator for all my classics and the boat. The overnight drainage gremlins have long hounded many of us. 

Do you have a phone or GPS charger plugged into your cigarette lighter because that doesn’t turn off with the ignition… not a lot but it will drain.

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any input for an increase in alternator output, instead of 13.5 idle to like 13.9, no matter what i try cant get it over 13.5/ 13.6 hot idle 950rpm, rev up stays the same!
old days we could adjust regulator output , but these newer self contained alt,s are a different animal!
i understand thats considered normal!

jdere, that is why i had the cable off over night, so to eliminate parasitic draw!

12.6 is normal, for a 12 volt lead acid battery: what is the voltage at 1200 rpm?

If that’s around 14.2-15, yer golden.

In my experience, a FULLY CHARGED 12V battery should read 13.2V but dropping to 12.9 is probably normal after some weeks. A good battery with no drains should hold a charge for many months in a room-temperature garage. Many alternators will charge the battery up to 14.5V or more, but this will slowly drive off water, so there’s nothing wrong with charging at 13.6-13.9V which should produce longer life. I am more concerned about the voltage dropping to 12.6 combined with weak starting. That sounds like a drain on the battery - you would know for sure after another day or two. Of course, make sure the terminals are clean and tight.

A typical, lead acid cell will give you 2.1V, a 12V car battery is 6 cells so you should see 12.6V in a healthy battery. Just after charging, you will see an over voltage figure for an open circuit battery, UnclePat’s figure of 13.2V sounds about right. This will drop over time, and when under load, down to 12.6V. If that isn’t enough to give you a good crank to start the engine then look at the high current path to the starter. Clean the battery terminals, and the posts on the starter and the solenoid. Also check the ground strap. Do you have a regular starter or a geared one?

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You could get one of these

…a true test of a battery is the specific gravity of the acid…someone can expand on that subject. .I’m too tired for theory this morning.

A few years ago, I ran a (#8) cable between the alternator output terminal directly to the RH connector on the heavy cable that runs across the engine side of the bulkhead. I did pick up some voltage, but can’t remember exact numbers. Easy enough to try!

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K good you mention back when 6V cars were normal !
i had a 1950 Cadillac 6v, when cold with 40W oil, would barely turn over , put an 8V battery ,turned up the regulator , and it made a world of difference , quicker turn, bright head lites , dash lites bright, made the car a better joy to drive!
wonder if someone were to make a 13V battery if it would sell, espcially for old big engines with heavyer oils?
my 1978 V12 calls for 20/50 oil!

Adding another cell would make it nominally 14V, actually 14.7V. You’d have to change the alternator to dump out a couple of more volts than that to be able to charge it. Not sure I’d like to run so much over voltage into the rest of the car’s electrical systems. Replacement ECUs aren’t a dime a dozen. I guess it may be possible to figure out a way of adding an extra cell into only the starter circuit, isolated from the main wiring loom, and with its own charging circuit. But most other people here don’t have these kind of engine turnover issues. I suspect you’ll only be papering over a real issue that needs fixing.

Engine oil technology has moved on a long way since then! No need to go crazy, but a lower weight, semi-synthetic is probably a better bet than, what will be expensive, “classic” 20W/50.

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Dave ,i did that with a #10 wire direct from output to Firewall stud post, about a year ago!
i just need a good 13Vs at the battery , after shut down, my car just is much better reacting to that!
what has me puzzled is the new Battery registered 12.95 vs when setting on the shelf for a month NO charger on it, before me getting around to install it!
after install and driving , then shut down , measures 12.71, that silly .25V s makes a difference
for starting and overall performance, even the ignition helps, (maybe hotter spark)!

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Cos , i do you castrol 20/50 Semi synthetic oil!
to add , when i run the battery down a little by Electric fans for about 5 minutes, the Alternator output reads 14.5 but in few minutes goes to 13.5V, shut off goes to 12.6/7, considered OK !
i also have a gear reduction starter, supposedly less power drag, spins fine tho!
if i could get the Alt, charge at a steady 14.5, not drop off to 13.5 when battery has come up??
i wonder??

Your voltage figures fit with all the cars I have owned in terms of the alternator output, open circuit values, shelf life etc. Bottom line is that if your car is not able to start properly or run correctly with a battery at a standard 12.6V, then there is something else wrong. Trying to artificially increase the voltage is just covering over the cracks.

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Cos, i do understand what you say, but MY car starts , runs , lights are ok,as is. but MY car does all those things better with 14VOLTS for them!
i thought someone may have fix like what i need, like a simple 14+ volts at all time when running!
and then the battery would be around 13V , setting overnight!
i’m checking into an alternator that has adjustable output voltage?

I would suspect your alternator is starting to fail if it wont charge over 14V. Just after a start you should see 14.5 - 14.7, tapering back to 14.1-14.3V as the battery comes up. I have a cigar lighter USB _ Volt display and find it reads low by 0.1-0.3V against a DVM. Clean all your grounds thoroughly - disconnect, clean, abrade, Deoxit, reconnect. Main battery ground cables in -ve earth cars are prone to corrode inside the weave if braided copper, and should be checked by comparing Volts at battery poles to volts from +ve pole to car body. If all thos doesnt improve your charge voltage, get the alternator checked,

I’ve put a new 110 Amps Alternator from a Land Rover Defender, it’s plug and play, just have to use your original pulley, and my calibrated Volt meter shows 14V under all conditions.

i run two #2 cables one off each side of engine, both grounded to body and sub frame!