I wouldn't rank glucose above fats. As I understand it, it's not exactly a "shorter battery" than fat - it is simply a form of energy that is abundant in plant life, but fat is still a (much) "better battery".
The reason our body always favors burning glucose first is NOT because glucose is "better" but actually because it is an inferior type of fuel (it creates "pollution" and is difficult to burn - you can develop diabetes from too much of it) - so our evolved system tries to get rid of it first, while hanging on to the "good stuff" for as long as it can.
The reason our body always favors burning glucose first is NOT because glucose is "better" but actually because it is an inferior type of fuel (it creates "pollution" and is difficult to burn - you can develop diabetes from too much of it) - so our evolved system tries to get rid of it first, while hanging on to the "good stuff" for as long as it can.