Originally Posted by fbconsults
Along these same lines, I just replaced my oem 12 v batteries with two six volt golf cart batteries hooked up in series to create 12 volts. The new batteries are 230 amp hours, twice as much as the oem.
Actually, if the OEM batteries were a pair of 115AH 12V wired in parallel, you'd have the same 230AH that your series wired 6V ones have now. The (wrong) assumption here is that the battery's capacity was measured the same way. If you carefully check a deep cycle battery, you MAY find the specification on a label that states how the AH capacity was determined. Many of the 115AH batteries I've seen, including ones from WM were tested with a 1A load on them. You should expect the "full" capacity of the battery, when used in your RV, only when it's feeding the parasitic loads on it during storage.
All batteries have internal resistance in them. The higher the current load placed on the battery, the more power is dissipated internally as a result of this internal resistance. Go check any battery manufacturer's web site and look at their graphs of battery capacity and you'll see that the capacity drops as the load increases. If you want to make your batteries look better than they are, then you rate them when testing with a 1A load. The traditional load test for rating a deep cycle battery used to be either a 10 hour (10% of capacity) or a 20 hour (5% of capacity) load test. The "reserve capacity" rating is supposed to be done by placing a 25A load on a fully charged battery and counting the minutes until the voltage, under load, drops to 10.8V.
Golf cart batteries are designed for severe abusive use, since once a cart leaves the clubhouse it won't come back until at least nine holes have been played. These batteries are ususally manufactured with thick solid lead plates, great for long life with a 10%-20% of capacity load. This construction also has the smallest plate area (compared to perforated thin plates) and the poorest capacity to provide 250+A to run a starter motor for 5-10 seconds. Their intended use makes them a great match for RV use.
I had problems with the batteries in my (new) 2011 327DS from the day it was purchased. The batteries had sat in the coach, fully discharged, for an unknown period of time before it was purchased. (There wasn't enough charge in the pair to start the generator.) After our first trip, the coach sat for a month with an unknown multiple amp parasitic load from the jack system on it. During our second trip, a cold weather one, we discovered that, on an overnight dry camp with the furnace running, the propane detector would trip due to low battery voltage. I finally tested one of the coach batteries and discovered that, when fully charged, it's actual capacity with a 10A load on it was 45AH. Both batteries were replaced just before the end of the 1 year FR warranty and I'm planning on the next set being golf cart batteries. When I install the golf cart ones, I'll also get one of the auto fill systems to keep the water levels up which will avoid my having to crawl inside the wall of the coach with a mirror and flashlight.
The house batteries box location on my coach is one of the biggest gripes I have with it. I think that at the next FROG rally in Goshen, I'll ask the factory techs to show me how they expect the owner to check the water level in the house batteries. It'll be interesting to see their answer.