Theoretical Portable PC Build

[Alaris44]

I know this question has been asked multiple times in the past, but lets just presume this would work. What rating of lithium ion(s) would be needed to run this setup for ~2-3 hours with an inverter? 120 W, high estimate https://pcpartpicker.com/user/Alaris/saved/YtNPsY

CPU: Intel - Core i5-7400T 2.4GHz Quad-Core Processor ($193.39 @ OutletPC)
Motherboard: Asus - STRIX B250I GAMING Mini ITX LGA1151 Motherboard ($108.99 @ SuperBiiz)
Memory: Corsair - Vengeance LPX 16GB (2 x 8GB) DDR4-3000 Memory ($154.88 @ OutletPC)
Storage: Samsung - 850 EVO-Series 250GB 2.5" Solid State Drive (Purchased For $98.94)

 

[popatim]

3hrs* 120w = 360wh
assuming 80% inverter efficiency 360/0.8=450wh
450wh / voltage of battery = amp-hour ;
so at 12v you need (450/12) = 37.5ah battery
for 14v batt (450/14) = 32.1 ah

Personally, I would doube the AH rating to account for battery aging over the long term (a few years)