Reading thru lots of threads, most folks seem to focus on the Amp Hour Rating of the Battery. I had read a few comments (without an explaination) that some folks think Reserve Capacity is more important. Your thoughts on what matters most?
Ask how the companies come up with the reserve capacity in minutes. Then ask how the amp-hours at the 20 hour rate are measured. Both are done on a fixed rate of demand. Neither one have much to do with "real life" use of a battery bank. They are only useful for comparing the "size" of the battery.
Reserve capacity is the number of minutes a battery can maintain a useful voltage under a 25A discharge. (i.e. down to 10.5 volts)
Amp hours is the most common unit used to express battery capacity. Amp hours are a product of current and time.
It would be rare for most rv'ers to draw 25 amps from a battery bank (exception if an inverter is used).
I would not worry which standard I used for comparing batteries. I.E. use reserve capacity or amp-hours at the 20 hour rate. Remember too, that they take the battery right down to 10.5 volts, or 100% discharged. We don't want to do that.
Here are some Peukert calculations to 50% (which is the lowest "safe" number) for a 400 amp-hour bank.
real life you can run the furnace for three days on a 25% duty cycle.
If I take the size down to 200 amp hours 50% numbers are:
155.5 hours @ 1 amp
10 hours @ 10 amps
3.4 hours @ 25 amps
real life you can run the furnace for a day on a 25% duty cycle
If I take the size down to 100 amp hours 50% numbers are:
68 hours @ 1 amp
4.4 hours @ 10 amps
1.5 hours @ 25 amps
real life the battery bank will be dead before morning on a 25% duty cycle for the furnace
It is almost always best to cram in the largest number of either amp-hours or reserve capacity minutes into the available space for the battery bank without exceeding the weight allowance for the compartment.
The best thing to do other than maximizing size is to do lots of conservation, for example changing to led lighting.
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Amp Hour rating is like RESERVE CAPACITY isn't it?
When saying "AMP" hour rating, one might be talking with AMPERAGE (starting capabilities) in mind.
And when saying RESERVE capacity, one might be talking about "how long battery will last drawing so many AMPs per hour capacity.
My guess is that there is a small technical difference between terms.
I know I carry Three (3) batteries wired in parallel, which are not the best arrangement BUT WORK for me. I also have a Trimetric 2025RV meter. Since I'm limited technically, I use this meter JUST to watch my current consumption and maximize my energy "reserves".
1 each Deka's Marine Master DP24 65 Amp/Hours
2 each Deka's Marine Master DC31DT 105 Amp/Hour 105/20 = 5.25 amps for 20 hours before dropping to 10.5 volts (dead)
Reading thru lots of threads, most folks seem to focus on the Amp Hour Rating of the Battery. I had read a few comments (without an explaination) that some folks think Reserve Capacity is more important. Your thoughts on what matters most?
Thanks
This website will give a clear answer to most battery questions in laymans terms.
www.dcbattery.com/faq.htnl
Harold and Linda
2009 CT Coachworks siena 35V
W-22 Workhorse 8.1L
Explorer toad
I too keep looking for documented info on how Series/Parallel battery connections deal with AMP Hours(AH) and Reserve Capacity(RC). Since I know absolutely nothing about any of this I find it is really hard for me to understand all of the answers out there about it. I am just a Southern Ill corn field dirt farmer who barely made it through High School where the teachers beat the******out of you behind the barn if you didnt learn fast enough. I got beat up alot hehe...
I finally found this simple chart published by Interstate Batteries which are manf by Johnson Controls and it helped me alot. This was the first chart I found that listed what happens to the RC capacity when connected in Series or Parallel.
(source Interstate Batteries)
Then comes the question what is the best battery combination to use.
My three GP24 12VDC batteries are connected in parallel.
The AH rating is 85AH... The RC rating is 115 minutes @ 25amps...
Using the chart above this tells me my three GP24 Interstate deep cycle batteries will give me 12VDC at 255AH with a RC of 345 minutes or 5.45 hours of drawing 25amps.
If you use two T105 6V batteries connected in series.
The AH rating is 225AH and the RC is 447 minutes @25 amps...
Using the chart above this tells me the two Trojan T105s connected in series will give me 12VDC at 225AH with a RC of 447 minutes or 7.45 hours drawing 25 amps. Connecting two groups of these T105s in parallel will give my 12VDC at 450AH and the RC of 894 minutes or 14.9 hours drawing 25 amps
If you use two GC2 6V batteries connected is series.
The AH rating is 220AH and the RC is 440 minutes @25 amps...
Using the chart above this tells me the two SAMS Club GC2s connected in series will give me 12VDC at 220AH with a RC of 440 minutes or 7.3 hours drawing 25 amps. Connecting two groups of these GC2s connected in parallel will give me 12VDC at 440AH and the RC of 880 minutes or 14.6 hours drawing 25 amps.
a recent comparison on here indicated that the three GP24 12VDC Batteries connected in parallel was a better deal to keep since you had the 255AH capacity.
I would think the two T105 6V batteries connected in series with the 225AH capacity would be the best deal since they will operate for 447 minutes or 7.45 hours drawing 25 amps compared to the three GP24 batteries only operating for 345 minutes or 5.45 hours drawing 25 amps. The AH rating of the three GP24 batteries is more than the T105s in series but the RC capacity is less.
Is this wrong thinking????
My Posts are IMHO based on my experiences - PM me Roy and Carolyn
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Amp Hours or Reserve Capacity, Which Matters Most?
If it is a starting battery, RC.
If it is required to store power and not provide cranking amps, amp hours.
2000 Sea Breeze F53 V10 - CR-V Toad
Some RV batteries live a long and useful life, some are murdered. Get a Digital Multimeter and Learn How to Use It
BFL13 wrote: The ratio of AH to RC is not the same at all.
Lets use your two different batterties and see which are best to use...
EG, my golf cart 6v GC2-XHD is 232AH and 475RC; but my "Starting/Deep cycle" 12v 27DC is 120AH and 180RC.
It takes two GC2-XHD in series to get 12VDC and your will have 232AH and 475RC or 7.9 hours running at 25AMPS.
If we added three of your 12VDC 27BC batteries in parallel you would have 360AH and a 540RC or 9 hours running at 25amps.
In this case the three 27BC batteries connected in parallel is a better battery bank then the two GC2s connected in series.
If you were using my three GP24 batteries with 85AH and 115RC then the totals would be a battery bank producing 12VDC rated at 255AH and a 345RC then the GC2 battery bank with the 232AH rating would be the better battery bank. The AH rating is lower than the three GP24 batteries but the RC rating is higher by a 135 minutes or 2.1 hours drawing 25 amps.
What is more important is to use the same standard.
The problem is this.. If you use amp hours. One company uses the "20 hour rate" that is to say if you figure out how many amps to draw so the battery goes from FULL to EMPTY in 20 hours, then use that number (Times 20) to calculate the amp hours. That's the 20 hour rate.. So one common battery is say 73 amp hours.
Another company uses the "one amp rate" that same battery, at 1 amp, might well list 90-100 hours.
And another company uses the "five amp rate"
NO STANDARD.
Reserve capacity is much the same.. Reserve after x,y, or z minutes.
Beyond that more amp hours, generally means more reserve capacity. But till they start standardizing the rating systems so they are all on the same page, The numbers you get from the store or manufacturer need serious adjustment.
Bottom line is for any given size and WEIGHT (Which is highlighted cause that is what counts most) the numbers for any two batteries will be so close as to be identical. No matter who made 'em or what type they are.
The other thing that is important is the TYPE of battery.. Starting batteries do not survive a deep discharge nearly as well as Deep cycle do, at least that is my expierence, Some argue with me and say they are all like, But others do a great job of explaining the difference.
Finally, Quality counts in years before replacement.. Trojan, for example, has a much better rep than say Wal-Mart,, but the difference in price.. Makes up for it.
Nothin adds excitment like something that is none of your business
Kenwood TS-2000 housed in a 2005 Damon Intruder 377
RC is generally minutes with 25 amp load t0 10.5 volts. Some cart batteries list 75 amp minutes. There are standards. Same with amp/hours although you do need the time base to be sure you are comparing similar specs.
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