Betavoltaics use transistors to trap electrons and appear to be too low amperage to be of any real world use.

Thermal batteries are used in space applications and in nuclear reactors, the search for a stable thermal isotope at room temperature would mean a generator. If such an isotope existed, an electric vehicle could have a generator on board to supplement the battery, meaning less battery overall and if one were to run out of range, they could simply wait for the generator to restore enough power to get to a charger. A stable thermal isotope at room temperature would be safe.

An even smaller application is to mimic the electric circuit, battery using an isotope to ionize copper at one side and fire electrons at the other side using an electron gun. The entire battery would have to be insulated so that electrons are sourced and forced from the electron gun and not from the surrounding air. This insulation is to contain the field, not against shorts. This mimicking the way electricity is produced without needing a force to dislodge the valance electron. If such a battery were possible it would be safe.

Unless you can advance the field, these technolgoies are not usable by simply building them in their current state.