Our conclusion is that the best thermal heat battery candidate among the 230 billion is 9 (3) with a predicted energy density of 0.38 kJ/g and a barrier height of 130.0 kJ/mol. For comparison the energy density of the parent system (0.14 kJ/g) is almost three times lower, while the barrier height (119.1 kJ/mol) is 11 kJ/mol lower. According to TS theory, an 11 kJ/mol increase in barrier height increases the half life by a factor of 85, i.e. from 3-39 hours (depending on solvent) to about 10 days -4 months. The computed absorption spectrum of 9 is shown in Figure , together with that of the parent system. Compound 9 retains an absorption peak abound 350 nm, but the intensity is reduced by about a factor of three.