You could probably use something like https://www.amazon.com/Nextrox-Converter-Regulator-Transformer-Waterproof/dp/B00BWKXTUU, a high power switching regulator. But that's also a bit of extra weight. Plus any kind of regulator/transformer will dissipate heat relative to the current you pull through it, so they're better for low-current applications. I think you'd need a really unusual reason to want this setup instead of just using a new 3 or 4s battery.