I have had some of the same type of questions rolling around in my head concerning LED lights I would like to add to my boat for night fishing.
I did a little bit of quick research this morning that I hope helps.
The first is a link to a site that helps you calculate the amp hours requirements for a specific amount of light watts at a known voltage. For instance...if you want to run a 100watt LED with 12 volts for 10 hours it will tell you how many amp hours it will take. It even takes into consideration if the battery is used in low temps and/or is older that 6 months. Once you have the amp hour rating you are looking for you match it up to a battery in the size and voltage you need.
https://www.batterystuff.com/kb/tools/calculator-sizing-a-battery-to-a-load.html
The second link is one for a video I found interesting on youtube concerning the current reality of cheap LED's that can be purchased on ebay. I am guilty of buying these and have a very affordable (aka "cheap") pair in my shop that I am disappointed with. I think this one is a must watch.
https://www.youtube.com/watch?v=vbt2ojkXPuo
The third link is just something for fun concerning led lights.
https://www.youtube.com/watch?v=-vgNh3fLxJc
Finally, I have many concerns about the quality of the light emitted from an LED. For some reason it always appears to me that the light does not drive through the atmosphere or water as strongly as an incandescent or metal halide light. I know for a fact I had to use one of my 40Watt LED spot lights this weekend when my normal spot light died on the water. We were getting so much light bouncing back from the moisture in the air that it was useless. It was a clear night in Texas and the incandescent spot light was giving no visual feedback from moisture before it died.
Anyhow....my two cents. Spend it as you see fit.
Rob