Question about Noco GB70 genius Boost

I have a vehicle that has not been started for 5 months, battery dead! 80AH battery is installed, and the vehicle has 5.2 litre capacity. Which Noco Genius do I need, and can I restart the engine 100% with it? Do I need a strong boost unit, or will GB20 or GB40 do? Many thanks in advance for any expert information! Greetings