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Old 27-05-2014, 19:49   #1
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battery ratingz

im looking at purchasing a cuople of new batteries looking at the interstate 6volt deep cycle golf cart batteries. the rating says they are rated for 232ah but this doesnt seem right to me i thought this particular size of battery was around 100ah. can someone please shed some light on this for me.
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Old 27-05-2014, 20:25   #2
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Re: battery ratingz

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Originally Posted by davevancat View Post
im looking at purchasing a cuople of new batteries looking at the interstate 6volt deep cycle golf cart batteries. the rating says they are rated for 232ah but this doesnt seem right to me i thought this particular size of battery was around 100ah. can someone please shed some light on this for me.
No, that's right: all 6-volt golf cart size batteries (GC2) are rated between about 210AH and 235AH. You have to combine two of them, in series, to get 12VDC @ 232AH.

Bill
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Old 27-05-2014, 21:58   #3
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Re: battery ratingz

i understand the series connection but am still unclear on one thing. if the batteries are rated for 232 ah this doesnt mean i can use 232ah that would just kill them wouldnt it.
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Old 27-05-2014, 22:01   #4
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Re: battery ratingz

With lead acid batteries, you don't want to take them to less than 50% charge on a regular basis and its hard to fully charge them, so figure that you can get 100 usable amp-hours from the two batteries.
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Old 28-05-2014, 07:18   #5
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Re: battery ratingz

thanks don thats what i thought but got confused when someone told me that the ah rating was how much i could use all the time.
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Old 28-05-2014, 07:49   #6
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Re: battery ratingz

The most commonly used rating for deep-cycle batteries is amp-hour (AH) capacity. It is calculated by C/20, i.e., how many amp-hours the fully-charged battery can deliver over a 20-hour period with a resistive load 1.20th the capacity of the battery (C/20) before reaching 10.5 VDC, whence the battery is effectively depleted.

For a 232AH rated battery, the resistive load would be 232/20 or 11.6 amps.

In plain language: take a fully charged battery, attach a 11.6 amp resistive load, and see how long it takes before reaching 10.5 volts. A fully healthy and fully charged battery should take 20 hours.

The above poster is correct. One doesn't normally use more than 50% of the capacity (i.e., don't discharge below 50% or 12.2VDC) before recharging. In practice while cruising, only about 35% of the capacity is really available for use, because that last 15% of recharging takes a very long time....too long for mechanical means unless motoring a lot.

So, effectively, house batteries on cruising boats normally cycle somewhere in the 50-85% state-of-charge range until plugged into shore power and given enough time to reach 100% recharge.

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Old 28-05-2014, 08:04   #7
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Re: battery ratingz

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Originally Posted by davevancat View Post
thanks don thats what i thought but got confused when someone told me that the ah rating was how much i could use all the time.
A rule of thumb based on the experience of many off the grid cruisers is you can safely use about 25-30% of the battery's rated amp hour capacity. This is set by lowest state of charge you can use without damaging the batteries and the highest state of charge easily reached.

So the min as Don noted is 50%. The max is set by your charging sources and the batteries. Once batteries reach about 80% charge the amount of additional harge you can put back into the batteries drops off a lot. Getting that last 15-20% charge could take hours and hours. If you are charging with engine or generator it just isn't worth while trying to get a full charge in. However if you have solar and/or wind charging capacity well in excess of your power use then you should be able to keep your batteries at a higher average state of charge.
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