Help with lead acid battery ratings


Senior Member
I have a question about the different ways that lead acid batteries are rated. I have a programmable battery charger that requires me to tell it, among other things,  the capacity of the pb battery in amphours but most automotive batteries are rated in Cold Cranking Amps, Cranking Amps and Reserve Capacity.
Does anyone understand battery ratings to help me calculate AmpHours when given only CA, CCA and RC? I need to charge a small battery with the following specs:
CCA 340 amps
CA 425 amps
RC 41 minutes
TIA, Mike.
Googling found this.  Looks from here like you should utilize the CCA number.
Personally here have one larger charger that has one low and one high amp charge and a few of the smaller chargers which utilize 1 or 2 amps that I utilize to trickle charge.
CCA, CA, AH and RC. What are these all about?
These are the standards that most battery companies use to rate the output and capacity of a battery.

Cold cranking amps (CCA) is a measurement of the number of amps a battery can deliver at 0 ° F for 30 seconds and not drop below 7.2 volts. So a high CCA battery rating is especially important in starting battery applications, and in cold weather.This measurement is not particularly important in Deep cycle batteries, though it is the most commonly 'known' battery measurement.

CA is cranking amps measured at 32 degrees F. This rating is also called marine cranking amps (MCA). Hot cranking amps (HCA) is seldom used any longer but is measured at 80 ° F.

Reserve Capacity (RC) is a very important rating. This is the number of minutes a fully charged battery at 80 ° F will discharge 25 amps until the battery drops below 10.5 volts.
An amp hour (AH) is a rating usually found on deep cycle batteries. The standard rating is an Amp rating taken for 20 Hours. What this means, say for a 100 AH rated battery is this: Draw from the battery for 20 hours and it will provide a total of 100 amp-hours. That translates to about 5 amps an hour. 5 x 20 = 100. However, it's very important to know that the total time of discharge and load applied is not a linear relationship. As your load increases, your realized capacity decreases. This means if you discharged that same 100 AH battery by a 100 amp load, it will not give you one hour of runtime. On the contrary, the perceived capacity of the battery will be that of 64 Amp Hours.
If the current drawn is x amps, the time is T hours then the capacity C in amp-hours is
C = xT
For example, if your pump is drawing 120 mA and you want it to run for 24 hours
C = 0.12 Amps * 24 hours = 2.88 amp hours
Cycle life considerations
C’ = C/0.8
Using first example
C’ = 2.88 AH / 0.8 = 3.6 AH
Here went to Black and Decker trickle chargers and keep them at 1 AMP.  2 cars have batteries sort of hidden in the trunk with posts going to the front.  They came with wiring kits (quick disconnects). 
Thanks but that doesn't help me to set the battery charger for this battery. It is a configurable charger for different types and sizes of batteries and one of the required settings is the capacity in AmpHour. i think htat it can be calculated from the Reserve capacity but I don't know the exact relationship between RC and AH.
This is a very neat charger that will charge the battery at a constant current until the battery reaches a pre-determined voltage(~14.5v)  at which point it will start decreasing the current and monitor the voltage as it drops. When the voltage drops to a voltage just slightly greater than the batteries resting voltage it will vary current to maintain that voltage indefinitely. Maintaing it just 0.1 - 0.2 above resting voltage is called a float charge or batery tender.
Step 9 from your link describes the charging procedure.

9.  The first step is bulk charging where up to 80% of the battery energy capacity is replaced by the charger at the maximum voltage and current amp rating of the charger. When the battery voltage reaches 14.4 volts this begins the absorption charge step. This is where the voltage is held at a constant 14.4 volts and the current (amps) declines until the battery is 98% charged. Next comes the Float Step. This is a regulated voltage of not more than 13.4 volts and usually less than 1 amp of current. This in time will bring the battery to 100% charged or close to it. The float charge will not boil or heat batteries but will maintain the batteries at 100% readiness and prevent cycling during long term inactivity. Some Gel Cell and AGM batteries may require special settings or chargers. - See more at:
A nice little charger that performs the same bulk, absorption and float charge procedure is the Battery Minder Plus. It does what the Hyperion charger does but it only  does it for lead acid batteries and at fixed charge rate. It is not configurable. They make one model for lead acid batteries and another for AGM type batteries.
I found this:
Many batteries today are rated in CCA or RC. CCA is Cold Cranking Amps. CCA is approximately equal to the RC of a battery times five. [1000 CCA is about 190 RC]. RC is Reserve Capacity. You can convert RC to amp/hours by the following formula:

Amp/Hours = (Reserve Capacity / 2) plus 16
Reserve Capacity is the generally the same as AH.
The general standard for AH is 20 hours, i.e. number of amps it can deliver over 20 hours.
So a 100 AH battery can deliver 5A continuously for 20 hours.
Reserve Capacity is calculated as a 25A draw until battery failure (10.5V).
To convert RC to AH, multiply RC by 0.4167.
In your case RC42 = 17 AH
From the Pacific Power Batteries FAQ
(Can't copy the link and can't make my typed link work)
Fixed link
Desert_AIP said:
Reserve Capacity is the generally the same as AH.
The general standard for AH is 20 hours, i.e. number of amps it can deliver over 20 hours.
So a 100 AH battery can deliver 5A continuously for 20 hours.
Reserve Capacity is calculated as a 25A draw until battery failure (10.5V).
To convert RC to AH, multiply RC by 0.4167.
In your case RC42 = 17 AH cycle battery faq/dcfaq4.html
Thanks for the reply. That is close to what I found in the link above but not just the same. Your formula puts AH at a little less than half RC and the formula I found puts it at a little more than 1/2 RC.  I suppose that I can call it approx 1/2 the RC and get the job done.
I learned something here today as I assumed that it was the CCA versus the RC that you needed to look at.
I do recall having to do this sort of stuff with my son's little cars; except it was me on demand relating to the batteries...
It seems to me that the bulk charge voltage, maintenance charge voltage and max charge amps are the critical settings. I wonder where the AH capacity comes into play at all when charging.
pete_c said:
Wierd all of the above posts are in a bold format; never seen that before.
That seems to have started when I posted some bold text from my clipboard but I have no idea why.