You must be a lucky person. Because, out of all the billions of billions of galaxies in this endless universe, you just happen to be in the right galaxy where there is a solar system with a single planet in it with sentient beings that eat metal (sodium and potassium)and you are on the right planet to get that question answered. Generations of people have come and gone for thousands of years here on the planet Earth, each one having played an important part in the principles regarding the answer to your question.
One of my own experiences with batteries was the understanding that its a chemical reaction. The battery does not store electricity. I know, amazing right? But true. The battery changes electric energy into a chemical energy and stores that when re-charging and vice-versa when dis-charging.
http://www.corrosion-doctors.org/Biographies/VoltaBio.htmDid you know that one amp is made up of of billions of billions of electrons but those electrons do not have the distinction of becoming an amp until time has passed?
http://www.corrosion-doctors.org/Biographies/OhmBio.htmThe history of humans on the planet Earth is full of names that have become synonymous with with the very lives we live in todays nuclear age. Names such as; Ampere, Faraday, Galvani, Hertz, Joule, Ohm, Tesla, and Volta just to name a few. In the field of medicine there is, what is know as an MRI or Magnetice Resonance Imaging and, as the name implies, it utilizes a very large and powerful magnet. These magnets can have different strengths according to what is to be imaged, wether it is a living patient or not, and the term Tesla is used as a degree of magnetic field strength.
http://www.corrosion-doctors.org/Biographies/AmperBio.htmKnow the load(s). For example: if I had a load of 2400 kW h's (kilowatt hours) at 120 vac (volts alternating current) and I want to know what that was in amphours at 24 vdc (volts direct current) I would simply multiply 2400 by 1000 and divide the answer by 24.
Watts is watts. There is no distinction between vac and vdc where watts are concerned in calculating loads.
So, know your load. All those billions of billions of electrical gizmo's on Earth typically have a label on them that will show at least two things, volts and amps or volts and watts. Less likely would you see amps and watts or even all three. Don't despair. As long as you have at least two you can figure the third by simple multiplication or division. One more critical item you must have is time. Liner time is critical to all electrical calculations of this type.
http://www.corrosion-doctors.org/Biographies/WattBio.htmAs for your other question.
120 x 10 = 1200
4 x 12 = 48
1200 / 48 = 25
25 x time? =?
I inverter inefficiencies can run as high as 15%. Also battery autonomy and longevity are important. Once you have the right amphour capacity needed multiply by a factor of 5. This will keep the batteries in the top 20% of full charge most of the time.
http://micro.magnet.fsu.edu/electromag/timeline/index.html There was one of those sentient beings that said something rather intelligent once. I cant remember which one it was but he said something to the effect of "give a child a fish, and they eat for a day. Teach them to fish and they eat for a lifetime,"
http://micro.magnet.fsu.edu/electromag/java/index.htmlWhen you look up at the stars at night, do you every feel a perception of depth in our universe? We know that molecular cohesion is what holds elements together as compounds, so couldn't gravity be constituted as molecular cohesion?
http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/index.htmlPity about Earth.
