"Add up the total current in a
"Add up the total current in amps that all the lights will take. Multiply that by the number of hours they will be on. That gives their consumption in Ah. Likewise multiply the current that the radio takes by the number of hours it will be on and add the two figures together.
Now multiply that total by two, because you dont ever want to run the battery more than 50% down and that will give you the minimum size of battery you will require in Ah.
The larger you can go above that the better because the less % of its capacity you use the longer the overall life will be.
Better still look at true deep discharge batteries because they can be run to more than 50% discharge without shortening their lives. A golf cart battery may be the solution. The downside of using a deep cycle battery may be that it may not be suitable for engine starting loads in an emergency
Whatever, never leave a lead acid battery in a partly discharged state for longer than can be possibly avoided or you will shorten its life expectancy. Recharge it right away.
You could also look at the feasibility of a solar panel or a wind turbine for charging."