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PostPosted: Mon Apr 19, 2021 6:02 pm 
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EFI Slant 6

Joined: Mon May 26, 2014 4:02 pm
Posts: 340
Location: Vermont
Car Model: Slant Six powered M37
I have a couple of spare batteries here that I am attempting to keep viable for when they are needed.

They both seem to settle down to a voltage around 12.40 to 12.46 after sitting for a few weeks. If I put a 4 amp charger on them, within 2-5 minutes they are acting as if their fully charged.. only to slump back down to 12.4ish volts.

What causes this, and is there a method of rehabilitating them? One battery is 10 years old.. the other is about 6 years old..


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PostPosted: Mon Apr 19, 2021 9:54 pm 
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Supercharged
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Joined: Thu Jan 27, 2005 8:32 pm
Posts: 7834
Location: SW Washington
Car Model: Fiat 500e
Those are old batteries, but the resting voltage isn't that bad. Load test them to see if they are any good. Lead-antimony batteries just don't last much more than 6-7 years and live a much shorter life if abused.

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PostPosted: Tue Apr 20, 2021 4:20 am 
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Board Sponsor & Moderator
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Joined: Mon Oct 21, 2002 11:08 am
Posts: 15362
Location: Blacksburg, VA
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12.4 V is not bad. I have run ones in cars that sit around 12.1 V for some time, assuming the weather is not too cold.

Lou

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PostPosted: Tue Apr 20, 2021 7:26 pm 
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EFI Slant 6

Joined: Mon May 26, 2014 4:02 pm
Posts: 340
Location: Vermont
Car Model: Slant Six powered M37
Dart270 wrote:
12.4 V is not bad. I have run ones in cars that sit around 12.1 V for some time, assuming the weather is not too cold.

Lou


That is all I need to hear!! I won't worry about them any more until they lack the energy to kick the starter over..

Joshie225 wrote:
Those are old batteries, but the resting voltage isn't that bad. Load test them to see if they are any good. Lead-antimony batteries just don't last much more than 6-7 years and live a much shorter life if abused.


Agreed. Newer cars seem to be especially hard on batteries.. and the riding lawn mower... I do not have a load tester.. But the starter might work as a practical load tester..


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PostPosted: Mon Aug 30, 2021 12:01 am 
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TBI Slant 6

Joined: Sun Jul 16, 2006 9:17 pm
Posts: 221
Location: NW New Jersey
Car Model:
Batteries chemically work by sulfating one of the plates (the anode is lead and the cathode is lead oxide). As you use battery power, the sulphur in the sulphuric acid turns to sulphuric oxide (the oxygen pulled from the water in the electrolyte) and plates the cathode plate, and produces electricity. When you charge the battery, the sulphate dissolves back into the acidic electrolyte. Over time, 2 things happen: the sulphate build-up gets too thick for the battery to function, and/or the sulphates flake off and fall to the bottom of the battery. If the pile of flaky sulphate gets tall enough, the flakes conduct electricity thus shorting adjacent plates (dead cells).

One trick to rejuvinate an older battery is to charge it to 15.2 volts. This requires a bit of know-how, but here is a site that offers an e-book that fully describes the process:

https://emediapress.com/shop/battery-rejuvenation/

Sorry if this looks like an ad, it's really not.

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