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Let say I have a battery that is a few years old.

When it was new, the specific gravity was indicating 1.265 when full, and it lasted fairly long.

If I do an equalization charge, for the same battery after 7-8 years, what would I expect to see?

  1. The specific gravity when fully charged will rise to the same level but it won't last as long.
  2. The specific gravity when fully charged will indicate degradation of the battery and will show a lower level (say - 1.215 or so).

Which of these answers is more accurate?

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1 Answer 1

up vote 4 down vote accepted

Neither choice is perfectly accurate and specific gravity is going to vary based on temperature and the quality/purity of electrolyte in the water over the life of the battery.

The fundamental change to a battery over it's life is that the internal resistance of the battery increases and therefore the same level of chemical charge will end up resulting in less delivered energy to the load. So, from that perspective, #1 is the most correct, assuming the electrolyte has not broken down and is in an ideal state.

However, in many practical circumstances, the electrolyte solution becomes polluted over time and the relative ratio of the water to acid mix changes making it hard to use specific gravity alone to assess the state of charge of the battery.

See this reference for some more specifics on the topic.

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thanks, @tall jeffIn. so for a lead-acid battery, can i replace the electrolyte? and if i can, what should be a reasonable usage for an electrolyte lifespan? does it varies in different conditions? –  Asaf Chertkoff Apr 22 '11 at 4:17
    
o.k. an addition for this great answer - the SG is not a capacity indicator, but only indicate the stat of charge of the available capacity - file:///home/asafche/Downloads/battery/carfaq4.htm#measure –  Asaf Chertkoff Apr 30 '11 at 14:37
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