The specific heat is the energy needed to raise the temperature per mass. So for water it takes 4.184 joules per gram to raise the temperature by 1 kelvin. So if you heated water to 75 degrees you would have put in about 205 joules per gram. You then have to deal with conductive losses and the efficiency of a heat engine.
This is not directly comparable to the energy density of gasoline or a lithium ion battery which use chemical reactions to store the energy. So you can turn almost 100% of the energy in a lithium ion battery into useful work but if you put the equivalent number of joules into heating an object you wouldn't get close unless you have a handy 0 kelvin object.
This is not directly comparable to the energy density of gasoline or a lithium ion battery which use chemical reactions to store the energy. So you can turn almost 100% of the energy in a lithium ion battery into useful work but if you put the equivalent number of joules into heating an object you wouldn't get close unless you have a handy 0 kelvin object.