size of battery needed for my solar panel

[JohnW2]

But what is start up?
1. cold start -18C
2. When it has not been used for 1/2 hour
3. When it ran 5 minutes ago

Any of those, depending upon what you want. I imagine that you would want it to be able to start under any likely conditions, so you would presumably want the battery to be able to do the 'cold start' - in which case it would obviously also be OK in the other situations you mention.

 

[cdbe]

Caravan and motorhome people tend to have more money than sense and throw thousands at huge power setups that seem to serve little purpose other than running a stinky air fryer and giving them bragging rights on the internet.

Unless you want to do the same, you'd be better with an LPG setup for heating/cooking/hot water etc.

I'd stop trying to "science" the electric, you have little idea of the heater consumption (if you chose to use it over a gas heater), or what your panel will produce in your location in winter - the typical start point for a caravan is (was) a 100w panel and a 110ah lead acid battery - start with that. As you aren't going to be there you should buy a cut off device that will monitor your battery and cut the power to protect it from excessive discharge. You will get a good idea from when you cameras shut down as to where you are and if you can monitor the battery voltage/charging time you can assess whether the panel will power a second battery or whether the battery needs a second panel etc.

The best leisure batteries I ever had were ex UPS batteries where someone was selling them off a pallet for £20 each, but that was before the off grid craze started.

 

[Harry Bloomfield]

Unless you want to do the same, you'd be better with an LPG setup for heating/cooking/hot water etc.

Even those, need some 12v power - my heating system, needs power to ignite, then power for the blown air distribution, cooking needs power for ignition, hot water needs power for the ignition, and pump.