Originally Posted by CrappyFishRman
I have a group size battery 24 and has 87 amp hours available. Best I can figure I could use my tv for 29 hours. Which would never happen, be more like 2-4 hrs a weekend if it's a rainy weekend. So we'd use very minimal.
Does this add up? I also plan on adding another battery which would help a lot. Thanks for any thoughts or opinions.
Only half of that 87 AH is available, or you will have a battery that won't hold a charge in very short order.
A true deep cycle battery can go down to 50% of charge hundreds of times without self-destructing. A combination battery (marine/deep-cycle) can handle a couple hundred 50% discharges before it is toast. A car starting battery will go maybe 6 deep discharges (50%) and it will be toast.
You also have other 12V current draws besides your DVD player/TV. Propane/CO detector, lights (LED lights help a lot), fans, fridge and water heater controls, water pump, and your furnace blower (usually biggest draw). A single size 24 battery (85AH) will not last more than 2 days without going below 50% with just normal loads, and will often only go 1 day.
Adding a second battery of the same size in parallel gives you the full 85AH, and up to 4 days if you are very careful with your usage.
That said, the DVD/TV draw is pretty small and won't make a lot of difference (6AH per day, 15% of your present capacity) if unplugged after a couple of hours a day. If you leave them plugged in, there will be parasitic current draws when not in use.