Long-lived power supplies for remote and even hostile environmental conditions are needed for space and sea missions. Nuclear batteries can uniquely serve this role. In spite of relatively low power, the nuclear battery with packaging can have an energy density near a thousand watt-hours per kilogram, which is much greater than the best chemical battery. Moreover, radioactive isotopes are available on the market for reasonable prices and low power electronics are becoming increasingly more versatile. Therefore, nuclear batteries are commercially relevant today. Literature review and theoretical considerations demonstrate that direct charge nuclear batteries have the highest efficiency converting radioactive decay energy to electricity when compared with other types of nuclear batteries. Direct charge nuclear batteries were chosen for this dissertation research. From calculations of the beta particle flux densities from sources of various isotopes, tritium and promethium-147 were chosen as the most suitable for building a direct charge nuclear battery. The theoretical analysis of factors influencing the overall efficiency of a direct charge battery with vacuum dielectric are outlined below. The estimated maximum efficiencies of tritium and promethium batteries are 12% and 21%, respectively. The main factors which effect the efficiency are the source construction, secondary electron emission and backscattering from collectors. Experimentally, it was demonstrated that the efficiency of the tritium direct charge battery model with vacuum dielectrics and collectors with secondary electron emission suppression and backscattering coating reaches 5.5%. This tritium direct charge battery model has an activity of 108 curies and demonstrated open circuit voltage of 5300 volts with short circuit current of 148 nanoamperes. The efficiency can be doubled with double-sided (4 [pi]) sources. A promethium-147 direct charge battery model of cylindrical design and double-sided (4 [pi]) source and collector having polyimide coating was built and tested. This model had an activity of 2.6 curies and demonstrated open circuit voltage at around 60 kV, short circuit current of 6 nanoamperes and efficiency of up to 15%. The experimentally demonstrated battery efficiency approached theoretical calculations. Also, the well known effect of charge accumulation in dielectrics under monoenergetic electron beam irradiation was utilized for making nuclear batteries. In this battery, charge accumulated in the surface region of a thick layer of dielectric from beta irradiation and was found to effectively conduct current through an uncharged dielectric. A simple nuclear battery model was fabricated and tested with a tritium source, a dielectric layer much thicker than the range of tritium beta particles, and a metal collector without vacuum space. This model, with 1 curie of tritium, produced 0.4 microwatts of electrical power on an optimal load resistor of 1 tera-ohm with efficiency approximating 1%. A phenomenological model describing the charging process is suggested in this dissertation and compared favorably with experimental data. Based on the described model, this type of battery having 1000 curies tritium would produce more than 1 milliwatt useful power with efficiency near 4% on a giga-ohm load. While the practically achieved efficiency of the solid-state nuclear battery is less than that built using vacuum dielectric, it is smaller and mechanically more robust.While studying the mechanism of nuclear battery charge accumulation in a dielectric, the space charge distribution in a dielectric under tritium irradiation was investigated both theoretically with calculations by Monte Carlo simulation code and experimentally with measurements by the Pulse Electroacoustic method. It was determined that charge accumulated under tritium irradiation in polyimide from the source-facing surface to a depth of approximately 5 microns.Possible applications of direct charge nuclear batteries and nuclear batteries with charged dielectrics are discussed in this dissertation. Experiments demonstrated the success of using beta batteries to power electrostatic screens for higher voltage alpha direct charge cells, and as spark sources for flash lamps. In the future, their use is promising for integrated electrostatic type motors and photomultipliers. Even ionizing radiation in deep space travel might be harvested utilizing this phenomenon.This dissertation discusses very promising research regarding the feasibility of a tritium nuclear battery with charged solid dielectric.