Mark_K5LXP said:
The devil is in the details but the statement "DOD doesn't significantly impact delivered Ah" stands on its' own. Back to the point of my original post, when you run the numbers for what are real world applicaton scenarios for RV's, DOD is not the predominant factor for battery life. Optimizing charge cycles, load leveling, and all the minutia of pack longevity can be mused and debated but one constant is with few exceptions in RV operating you're never going to burn through all the available cycles a deep cycle battery has by running down to 80% DOD nor are you buying anything by setting a higher arbitrary threshold. The "50% rule" virtually assures you will be inconveniencing yourself through reduced run time, not using capacity you paid for up front and for those that think they're ahead of the game by buying twice as much battery, they're only paying more up front and banking even more capacity that will go to the recycler unused when it's time to replace the pack.
Mark B.
Albuquerque, NM
I see we agree in a number of areas and disagree in some areas.
Here is a link to a Trojan Battery PDF file showing the number of life cycles for their AGM battery.
https://www.trojanbattery.com/pdf/TRJN-0255-SOLAR-AGM-Flyer.pdf
Or if you prefer here is a link to the same information on their website:
https://www.trojanbattery.com/solar-agm-2/
It is good to note that the chart shows that their battery if only discharged 20% (i.e. 80% full) it will get 4500 discharge/charge cycles. However discharge it 80% (20% full) and you only get 1000 cycles.
I don't have enough detailed data to truly know if someone would get the identical number of AH's in the life of the battery, if you take 2 batteries, one being 80% discharged and the other only 20% discharged. I do question if the batteries are truly capable of sustaining their rated AH's for the life of the battery if "run hard and put up wet" on a continual basis.
But then again maybe most RV'ers wouldn't care if they only got 1000 cycles if they only dry camped or boondocked for 5 day or 30 days of a year. The battery would outlast the life of their use of the RV. Or they would ruin it by accidentally totally discharging it, or significantly overcharging it.
It is also good to remember that someone designing their system to use 80% of the battery on a daily or almost daily basis will run into problems getting back to the 100% full to start their new cycle for the next day.
Only getting back to 80% full and now you now longer have the 80% capacity to use. You are down to only having 60% capacity to use instead of the 80% you planned for your system.
If I installed 400AH and planned to use 320AH the first day and can only charge the system to only 320AH capacity (80% full), I now only have 256AH and I really need the 320AH for my life style. OOPS. Kind of a problem. 2nd, 3rd, 4th day and beyond I am missing lots of AH I had planned on. What happens if I can't run my generator as long, or if using solar, I have a rainy day or several rainy days. Now what do I do.
Bottom line, I guess all the above doesn't matter since for the "life of the battery" I will get the same number of AH in that "life of the battery".
Yep, the "devil in the details" comes into play.
A few more details:
-- A lead acid battery starts off at 12.6V when fully charged. However when down to 30% full, the voltage is only about 11.75V.
-- A battery at only 11.75V or even 12V and now you want to put a heavy load on the battery pack to run the microwave/hair dryer/coffee maker or whatever device or devices which you want to use, you probably have a problem.
-- Voltage sag. Put a load of 20%-25% (or even 10%) of the capacity of the battery and the voltage drops. Inverters are not happy with very low voltage. For one it stresses the components. Another there is usually a low voltage cut out that could keep you from powering whatever with the inverter. Many inverters allow you to set a very low battery voltage cutout but you stress the inverter components even more.
Anyways it is an interesting discussion. No simple answer or one size fits all.