Batteries are rated at 20 hours for most amp hours.
So depending on the battery a 100amp hour deepcycle should give you 100amp hours total over a 20 hour time period. That would be 5amps per hour discharge rate times 20 hours. If you run it hard for 3 hours though it may only give you a total of 75amps, 25amps per hour times 3 hours. So you lose 25amps available power from that rating.
Something like that and varies by battery, but normally figured over a 20hour period.
I saw a chart for it from a battery website awhile back but can't find it now. Showed the power we should expect from the battery over various hours of discharge rates, but the amp hours shown on the battery were figured at 20hrs and alot higher than you would get draining it in just 3 hours.
On the 20hour amp ratings, I also got to thinking about spacing out my loads a bit now for more power from the same size battery banks. Don't know if it helps or not, but I figure when easily done and convient run things one at a time. Sort of spread out the load for a longer time at less amps than all at once at high amps, even though my batteries and inverter could handle everything at one time fine.
For example, my coffee pot is about 1500watts or 125 amps at 12V. Lets say my aircompressor is the same thing. Running both at the same time I am drawing 250amps per hour (if they both actually run continously that long). If my battery bank is 1,000amp hours rated over 20 hours, then that's a 50amps per hour rating for the most power. I am drawing 5 times that if I make coffe and fill the compressor at the same time for an hour straight. I probably only have about a 700-800 amphr rating on the same battery bank at 4hrs (probably even less). So I could have 1000amps at 50amp per hour over 20 hours or maybe 700amps at 250amps per hour for less than 3 hours.
Now what I am thinking here is how much power in amp hours will I actaully lose if I run everything at once for that 250 amps per hour compared to making coffee first at 125amps then when that's done fill the aircompressor at the other 125amps per hour.
Spreading it out this way for a longer period of lower amps gets closer to the 20 hour rating, even though I am still more than double the rated 50amps I am far less than the 5 times if running everything at once. Of course these two items only run about 10-15 minutes each, but still how does that effect the total amp hours of the battery bank if running them at the same time 4-6 different times durring the day?
That would add up to the 250amps for one hour, but spread out over time not all at once.
In the above example those two high power items only run about 10-15 minutes each probably, but what about adding things like a clothes washer and other high demand items also. If drawing power from the battery bank fast like that reduces the total amps hours it will produce, then how much power are we losing when we run several high power items at once for shorter times?
Even though I have a 5,000 watt inverter and I think they are supposedly more effceint when run near full power output, what is the effect on the battery bank in lost amp hours when doing so? Will spreading out the load like say making coffee, then filling the air compressor, then washing the clothes add amp hours to the battery bank (availble for the entire day) and more than compensate for the less than efficent use of the inverter at lower loads. Or would drawing high loads for shorter times be better and average out durring the day.
I am thinking smaller loads spread at durring the day would be far better. Also this is figuring high amp hour battery banks like 1,000 or above of course.
For those with the small banks (like statring out) would running smaller loads over longer times also help get the most amp hours total. Like 200amphr bank and 300watt inveters running 12amp loads onger compared to shorter 25amp loads.
