Rubidium is a heavy alkali metal, therefore people are not that interested to go towards these elements. The energy is given in Wh/kg, this means anything that might make the battery heavier will limit the energy of the cell. Moreover, in an ion battery the rubidium ion would be far too big. It has double of the size of an lithium ion. This limits the movement (diffusion) and the final uptake of the rubidium in the electrode host.There might be ideas to use small concentrations of this in order to modify the electrode performance.
Helium is a noble gas and most of the time inactive. There might be attempts to use liquid helium in thermal batteries but it does not seem to succeed.
Summing up, for most battery applications, these two elements are not eligible.