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Bald Camper

Member
Joined
Jan 21, 2023
Posts
6
Location
Quebec
Cranking amps is different from the capacity of a battery, It's a complicated rating which is a function of both the battery capacity and the battery internal resistance. It is a useful rating for the engine battery, but it is totally useless when talking about the house batteries, which don't even have such a rating.

It is possible to talk about either the current capacity of a battery, or the power (current times voltage) of a battery. However, the power capacity isn't often used.

From the Trojan Battery Company:
What are the 20-hour and 100-hour rates?
The 100-hour rate is just an index that is used in the battery industry to compare batteries of different types and sizes. The 100-hour rate is the amount of Ahs the battery will deliver during a 100-hour discharge. The capacity of a battery, in Ahs, is a dynamic number that is dependent on the discharge current. For example, a battery that is discharged at 10A will give you more capacity than a battery that is discharged at 100A. With the 100-hr rate, the battery is able to deliver more Ahs than with the 20-hr rate because the 100-hr rate uses a much lower discharge current than the 20-hr rate. Both rates are used as baselines in different parts of the world. Either rate, however, will give you the same view of a battery. A higher capacity battery will have higher 5 and 20 hour rates than a battery with lower capacity.


From Wikipedia:
A battery's capacity is the amount of electric charge it can deliver at the rated voltage. The more electrode material contained in the cell the greater its capacity. A small cell has less capacity than a larger cell with the same chemistry, although they develop the same open-circuit voltage.[50] Capacity is measured in units such as amp-hour (A·h). The rated capacity of a battery is usually expressed as the product of 20 hours multiplied by the current that a new battery can consistently supply for 20 hours at 68 °F (20 °C), while remaining above a specified terminal voltage per cell. For example, a battery rated at 100 A·h can deliver 5 A over a 20-hour period at room temperature. The fraction of the stored charge that a battery can deliver depends on multiple factors, including battery chemistry, the rate at which the charge is delivered (current), the required terminal voltage, the storage period, ambient temperature and other factors.
 

Bald Camper

Member
Joined
Jan 21, 2023
Posts
6
Location
Quebec
Cranking amps is different from the capacity of a battery, It's a complicated rating which is a function of both the battery capacity and the battery internal resistance. It is a useful rating for the engine battery, but it is totally useless when talking about the house batteries, which don't even have such a rating.

It is possible to talk about either the current capacity of a battery, or the power (current times voltage) of a battery. However, the power capacity isn't often used.

From the Trojan Battery Company:
What are the 20-hour and 100-hour rates?
The 100-hour rate is just an index that is used in the battery industry to compare batteries of different types and sizes. The 100-hour rate is the amount of Ahs the battery will deliver during a 100-hour discharge. The capacity of a battery, in Ahs, is a dynamic number that is dependent on the discharge current. For example, a battery that is discharged at 10A will give you more capacity than a battery that is discharged at 100A. With the 100-hr rate, the battery is able to deliver more Ahs than with the 20-hr rate because the 100-hr rate uses a much lower discharge current than the 20-hr rate. Both rates are used as baselines in different parts of the world. Either rate, however, will give you the same view of a battery. A higher capacity battery will have higher 5 and 20 hour rates than a battery with lower capacity.


From Wikipedia:
A battery's capacity is the amount of electric charge it can deliver at the rated voltage. The more electrode material contained in the cell the greater its capacity. A small cell has less capacity than a larger cell with the same chemistry, although they develop the same open-circuit voltage.[50] Capacity is measured in units such as amp-hour (A·h). The rated capacity of a battery is usually expressed as the product of 20 hours multiplied by the current that a new battery can consistently supply for 20 hours at 68 °F (20 °C), while remaining above a specified terminal voltage per cell. For example, a battery rated at 100 A·h can deliver 5 A over a 20-hour period at room temperature. The fraction of the stored charge that a battery can deliver depends on multiple factors, including battery chemistry, the rate at which the charge is delivered (current), the required terminal voltage, the storage period, ambient temperature and other factors.
Is-there a problem with hocking 2 6 volts battery in series if there is a small difference in battery capacity.

Thank-you
 

Mark_K5LXP

Well-known member
Joined
Nov 17, 2018
Posts
3,314
Location
Albuquerque, NM
Is-there a problem with hocking 2 6 volts battery in series if there is a small difference in battery capacity.
Yes. Technically the same number of Ah will be discharged and charged into both batteries but the smaller battery will be more deeply cycled. There are subtleties of charging a disparate pair like that too but suffice it to say the larger battery is going to beat the smaller one all to hell. Depends a lot on what you mean by "small difference". There are no two identical batteries and minor differences of a few percent aren't usually significant. Over time you'll see batteries diverge in a few different ways so even if they start out the same they don't end up that way. The less current, and less deeply they're cycled the less any difference they have will have an impact. But put say a 100Ah in series with a 200Ah, and you're going to have problems right out of the chute.

Mark B.
Albuquerque, NM
 

Bald Camper

Member
Joined
Jan 21, 2023
Posts
6
Location
Quebec
Yes. Technically the same number of Ah will be discharged and charged into both batteries but the smaller battery will be more deeply cycled. There are subtleties of charging a disparate pair like that too but suffice it to say the larger battery is going to beat the smaller one all to hell.

Mark B.
Albuquerque, NM
Thanks so much
 
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