Power Consumption

That must be a very small TV.

In short, the answer is no. You cannot measure how many amp hours are left in a battery. You can get a thing called a watt meter, which can be used to measure how many AH have been used compared to how many AH have gone in which gives a rough guide as to how many are left.

Yes, about 11.2 volts indicates a flat battery. Yes, 13.8 is close enough to fully charged.

Have a look on the back of the TV. See what watts it is. Watts divided by volts = amps. Work out all the amps for everything you want to use. Then double that figure so that you have room to spare. Then the solar panel you want will be twice the amps of your doubled amp usage figure...If you do that you have plenty for later if you want to add a fridge or a fan or a lap top etc.

For example, if all the things added up to say 1.5AH. Then your double is 3AH. So your panel would want to be capable in perfect conditions of making 6 amps, or if you like an 80 watt panel.

A fully charged rested battery is 12.7 volts not 13.8.

13.8-14.5 volts is the output of most alternators that charge a battery but the voltage will reduce with no load to 12.7 volts.

12volts is about 50% of fully charged.

11.4 volts is generally accepted as the lowest you would wish to drop a battery to for longevity and the lower you go the fewer cycles the battery will be capable of.

I believe you will need a 120watt solar panel as the realistic output is just over 6 amps.
Have a read of this and his other articles which I believe to be accurate.

http://www.campertrailers.org/collyns_page.htm#Lead
Regards Philip A

It seems like you are pretty right for a week camping..

Next time you go camping, check the voltage after running one of the appliances for approx 1/2 hr ( with nothing connected when you check the voltage ) and that will give you a starting point.....then once a day, check the voltage and see how far down it gets over a week..

11.8 to 11.9V is generally accepted as the lowest you want to go on a regular basis..

Next trip, see how you go without a solar panel, but if you can borrow one, keep it as a backup just in case..

This may be of use, it gives a rough idea of the SOC of a battery with a small
load connected to it.

SDG

As advised by all the others 12.7 volts is a charged battery.
With the draw your talking about you could get away with a 60 watt panel but i'd advice an 80 watt panel for those dull days.

I see no mention of an elec fridge in your post (you don't have to have one) and the 80 watt allows for future upscaling.

The important thing is to keep the volts as high as you can for as long as you can in your batt so don't fall in to the trap of trying to work out how long you can drain your batt before you connect the solar panel.

The moment you get to camp set up the solar panel. You cannot over charge the batt with a quality panel and regulator. The Regulatoer will only provide that power that is required by the batt based on usage and it is free to do so.