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Open Roads Forum  >  Tech Issues

 > Single AGM or 2 GC2???????

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Sam Spade

North Central Florida

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Joined: 11/05/2015

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Posted: 10/12/17 12:13pm Link  |  Quote  |  Print  |  Notify Moderator

wa8yxm wrote:

What's more AGM's are SEALED Valve Regulated Lead Acid. Adding distilled is NOT an option Thus the total life tends to be less than with Flooded types.

That is exactly the OPPOSITE of everything I've read, heard and experienced with AGMs. Which is that they typically have a useful life TWICE as long in most practical applications.

Could you please provide some reference for the claim "total life tends to be less" ??


las peƱas, michoacan, mexico

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Joined: 06/01/2007

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Posted: 10/12/17 01:46pm Link  |  Quote  |  Print  |  Notify Moderator

I hesitated writing this as I feel strongly it would be a waste of time.

Professionals compensate for abnormally high ambient temperature by adjusting the specific gravity of cell electrolyte.

Adjustment means less dense specific gravity. More water less acid. A higher percentage of water.

In this case I would recommend a final specific gravity of 1.260
Equal to a .025 reduction in density
Means a fully charged battery measured with a hydrometer will be 1.260


  • Cell electrolyte must be diluted with distilled water
  • All cells MUST be equal in density
  • The best way to do this is to wear gloves and googles
  • Carefully empty all six cells into a plastic vessel
  • Five gallons capacity would be ideal
  • Measure specific gravity as it sits
  • Start adding distilled water
  • Stir thoroughly after each tweak with water
  • Measure gravity after EACH addition of distilled water
  • Slowly but surely dilute the electrolyte to 1.260
  • If you bumble and gravity ends up at 1.258 don't sweat it

What's left in the plastic container is HAZARDOUS WASTE. Seal it tight. Many battery places will accept it because it is stated as being BRAND NEW ELECTROLYTE.


  • At temperatures of 90F adjusted density will maintain same spec performance as the battery did with original acid at 68F
  • Battery life is at the very least DOUBLED (expect 250%) at elevated temperatures
  • The advantage increases as the temperature exceeds 100F to 110F
  • The battery can be "more safely" charged at extreme temperature.

    SAFETY FIRST! Please do not even think about doing this without using goggles and plastic gloves.

Gassing, corrosion is dramatically reduced in lieu of reducing charging voltages. However to make this perfectly clear HOT acid eats plates regardless of voltage. Only weakening the potency of acid reduces plate corrosion to "normal" amounts.

A battery DISTRIBUTOR such as the regional INTERSTATE battery distributor may or may not be willing to do this for a price. Only you can decide whether or not 250% increase in battery life justifies the hassle or labor cost.

Professionals label this adjustment as being TROPICAL BLEND ELECTROLYTE

* This post was edited 10/12/17 02:00pm by MEXICOWANDERER *


Regina, SK, Canada

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Joined: 12/18/2004

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Posted: 10/12/17 03:47pm Link  |  Quote  |  Print  |  Notify Moderator

Hi Mex,

Very nice post--thanks for sharing your knowledge with us.

Regards, Don
Full Time in a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.


surprise Az.

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Joined: 06/20/2009

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Posted: 10/14/17 08:52pm Link  |  Quote  |  Print  |  Notify Moderator

Sam Spade wrote:

HTElectrical wrote:

Probably 2 Costco GC2 batts again. Correct???

I have a charge wizard, but since I only slightly discharge them, the only reason to use the Wiz, is to boil of the Sulfation that I cause.

Despite the quoted opinion, I think AGMs are always a better choice unless your budget is REALLY tight.

Given the usage pattern your describe, one large 12 V "deep cycle" AGM probably can be had for about the same price as replacing the two that you presently have.
No need to add water, virtually no sulphation and no corrosive gasses escaping to corrode things nearby.

All wet cell batteries are subject to sulfating, including AGMs.

Harold and Linda
2009 CT Coachworks siena 35V
W-22 Workhorse 8.1L
Explorer Sport toad

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