Hybrid battery goes from full chg to near flat VERY rapidly.

There is not so much similarity to the Prius HV battery and a laptop battery, as far as the battery management ECU is concerned. In the Prius, there are many taps on the series string of modules that make up the battery pack, and each one is monitored for variations in internal resistance and capacity. If one module diverges appreciably from the rest, then you get the sort of behavior that you describe- fast changes in charge level on the MFD. Some have had DIY success in changing out the weak module, but the manufacturing tolerances of the HV battery are such that the next weakest module will sooner or later be apparent. Those who depend on the car are recommended to buy a rebuilt pack and replace the whole. It depends on your particular DIY enthusiasm.

Reading the particular DTC that you are getting and reporting it here will be of use to others in diagnosis. Also, listing your general location in your profile will help.