[Milsurplus] Lead Acid Batteries

[D C Macdonald]

Manufacturers of sealed lead-acid batteries generally
recommend a "float" charge of 2.25-2.30 Volts per cell.
This should provide a life span of four to five years until
the capacity drops to 60% of original rating.

Self discharge (open circuit) runs around 3% per month
and an annual charge is sufficient to maintain the original
capacity of a battery not in use.

Optimum temperature is 60-77 degrees F.  Estimates of
battery degradation are battery life decreased by 50%
for each temperature rise of 18F above room temperature.

Open circuit voltages (per cell) when fully charged and
discharged are 2.15 and 1.94 Volts respectively.

Recovery is possible from a "rapid" full discharge, but
unlikely from a continuous "slow" full discharge.

This above info is paraphrased from the "user guide"
from manufacturer "POWERSONIC."

My own experience as a comm technician with FAA is that
these will quite easily last 4 years or more with proper
care (correct float charge and  NO  overcharge).

73  ---  Mac, K2GKK/5


----Original Message Follows----
From: Peter Gottlieb <nerd at verizon.net>
To: Milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] Lead Acid Batteries
Date: Mon, 07 Feb 2005 10:06:44 -0500

I hate to beat a dead horse but I just wanted to point out a few things.

First of all, there are very few "gel cell" batteries out there.  Gelled 
electrolytes just never became popular, perhaps due to ionic mobility 
issues. What IS common though, are batteries where the liquid electrolyte is 
absorbed in  porous glass or other mats between the plates.

Lead acid batteries must remain charged or (mostly) irreversible sulphation 
of the plates will occur.  Mild sulphation can be reversed but lead sulphate 
is larger than the material it replaces and eventually the plates will swell 
and can short through the insulating mats and even crack the battery case.  
Some UPSes used to have tight fitting battery compartments and the swelled 
batteries were impossible to remove after the steel chassis were deformed.  
Obviously the batteries do not need to be on float continuously but they 
cannot be allowed to completely discharge.

My understanding from Yuasa, Panasonic and CSB (China Storage Battery) is 
that the absolute best charging method is to constant voltage charge to 14.2 
or so until the current tapers to a low value then drop to a maintenance 
float of 13.7 or so.  Very close second best is to constant voltage charge 
to 13.7 and this is what is mostly done.  How much better the higher voltage 
is depends on the engineer you talk to with some saying it is insignificant 
and others saying it promotes better cell charge balance and faster charge 
but at the risk of overcharge and possible gas generation and venting 
resulting in moisture loss and internal terminal corrosion.

Battery construction is a compromise.  Float and charge/discharge cycles 
take their toll on the plates and to get longer life you need heavier plates 
but this reduces surface area and thus capacity and conductance.  A heavily 
used battery might only last 3 years while one in float standby service can 
get 5 years of life but that is about it.  Longer life batteries are 
available but they are larger for the same capacity.  I have seen batteries 
guaranteed for 25 year service life and have no doubt they can achieve that 
but those are larger than you want to carry with you in a manpack.

Peter


gl4d21a at juno.com wrote:
>I was interested to read the comment about keeping lead acid batteries 
>charged.  I was recently in communication with a manufacturer of commercial 
>equipment about the treatment of the gelled electrolyte batteries in his 
>equipment, and he recommended leaving them on charge no longer than a 
>couple of days at a time.  So, a blanket statement about keeping them 
>charged needs a lot of modifiers, and humming and hawing.
>
>A number of years back I designed some equipment for a customer which used 
>gelled electrolyte batteries, and I found a charger manufacturer who could 
>supply a dual rate charger which initially charged at 14.something volts 
>until the current dropped to a preset value, then dropped to a maintenance 
>charge of 13.something volts.  Both voltages need to be temperature 
>compensated, and set to the particular electrolyte chemistry.  So, the 
>comment about a bad idea which went downhill from there about lead acid 
>batteries in electronic equipment is well justified.  Way too many 
>variables to be practical.


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