Directory:Batteries:Most Ah ratings are incorrect

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'In Reference to Bettery Involvement in John Bedini's "OS:Bedini SG"'

Most Ah Ratings are Incorrect

From: "roamer1952004"


Sent: Tuesday, October 26, 2004 2:05 PM

Subject: [Bedini_SG] Most Ah ratings are INCORRECT

Most lead-acid batteries are MISlabeled with a higher Ah rating than

what they really usefully contain.

UNLESS you get a true deep-cycle battery, you're not getting what you


Gel-cells are usually WAY overrated on useful Ah. The rating on the

battery probably also includes the BTU's you'd get if you were to set

it on fire after you powered your load with it.

For any "regular" lead-acid battery with a CCA rating, just divide

that CCA number by 20 and you'll have it's true Ah capacity.

But, STARTING BATTERIES are not deep-cycle worthy. So, you can only

have the first 20% of that CCA/20 figure without damaging that

battery. As an example, a 600 CCA battery has 600/20 = 30Ah. Then take

that 30Ah/5 = 6Ah of usable charge without damaging the battery.

Short answer is, DON'T bother with starting batteries, except for

STARTING things.

Just buy deep-cycle batteries and be done with it for your storage

bank needs.

In any case....

You don't need a lab to know approximately what you can get from a

battery, just a CONSTANT CURRENT load.

Electrical charge is defined in measured quantities of electron charge

called COULOMBS.

"Charge" in a battery is defined as Ampere-hours.

ONE "ampere" is defined as ONE COULOMB PER SECOND of "flow".

So, you COULD write this as (Coulombs per second)-hours.

"Ah" is much simpler.

Forget the "voltage" except as a starting and finishing point

measurement. The batteries are rated in Ah NOT Watt-hours. Ah only

considers the COULOMB content of the battery, not the voltage at which

it is released.


1. Start by using 80% of your Ah rating as your REAL USEFUL CHARGE

CAPACITY. This means a 100ah battery should be considered an 80Ah

battery. Got it? Good.

2. Divide that 80% number by 20. So it's 80Ah/20 = 4 amperes. You

can draw a steady 4 amperes for 20 hours from a 100Ah battery without

damaging it.

3. Apply the 4amp load to the battery for 20 hours. Then remove the

load and see where the battery voltage pops up to.

If it's below 12v, then the battery's labeled rating is wrong.

Recharge the battery with a charger that can get it's voltage up over

12.6v within a couple of hours. If it takes longer than that to get

over 12.6v, the battery is already beginning to sulfate.

See also

Directory:Bedini SG:Battery Characteristics - listing as part of the Bedini SG project.

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