Direct charge nuclear battery(DCNB) has a low efficiency in converting decay energy into electrical power.In this paper

by analyzing structure and working principle of a DCNB

we give its equivalent circuit

from which the charge function and simplified models of DCNB in different load resistance conditions are obtained for calculating the battery output power.The maximum output power and voltage-current curve of simplified model agree well with the measured data in Ref.[2].Methods of choosing suitable load and increasing charge current for improving energy conversion efficiency of DCNB are presented.And discusses are given for optimizing the source efficiency and geometrical factor

and for reducing the secondary electron effect on the chare current.