Thermo-electrochemical cycles.
The idea is simple: the favorability of a chemical reaction is a function of temperature, some reactions are more favorable at high temperatures, some at lower. For electrochemical reactions (e.g. batteries) this means a change in voltage at different temperatures. Some reactions have higher voltages, some lower. By choosing a pair of redox reactions such that the direction of charge transfer can be reversed within a specified temperature envelope, one can create a thermal engine that directly converts heat to electrical energy without requiring a turbine.
There’s lots of research on this, sometimes called the ‘omnivorous’ flow battery.
If they weren’t a fascist ethnostate led by a madman, they probably wouldn’t have launched the war in the first place. The utterly misguided belief in their superiority is what made them blind to the (rather obvious) conclusion that they didn’t have the resources to conquer Europe (mostly) single-handedly. Let alone take Italy along with them.
Hell, the only reason it was even - somewhat - close at points was Hitler’s insistence on a blitz through the Ardennes to attack France. The generals thought it was a terrible plan (and it was, that’s a big reason why the French were unprepared and got essentially knocked out of the war in weeks).
WW2 is interesting precisely because the big numbers only point one way - a complete defeat of Germany and Japan by much larger and better-supplied powers. But there were multiple points where tactical developments could have become strategic victories - which are rather rare occurrences in the study of war.
E.g. the Nazis didn’t have the resources to conquer the Soviet Union, but if the battles of Stalingrad and Moscow had gone their way, it is difficult to see how the USSR could have maintained a functioning government. Likewise Japan was woefully under prepared to defeat the US in the Pacific, but if the US carriers had been sunk at Pearl Harbor, maybe the Japanese hedgehog strategy to fortify the Pacific islands works out.
Of course, once the bomb was ready then nothing else matters.
Ultimately, it was all massive tragedy the likes of which I hope we never see again. The counterfactuals are fun to play out, if you can abstract away the millions of deaths in all sides.