Um if you are using a 12V screen then use a standard gel battery or better still on of those Lithium packs that come with a charger from EBAY or the likes . They are light for mobile applications give you a nice power level and cheap enough you will need to use a small switch mode module for the 5V output.You should be safe on assuming 85% efficiency in what ever calcs' you are doing !
Um if you are using a 12V screen then use a standard gel battery or better still on of those Lithium packs that come with a charger from EBAY or the likes . They are light for mobile applications give you a nice power level and cheap enough you will need to use a small switch mode module for the 5V output.You should be safe on assuming 85% efficiency in what ever calcs' you are doing !