Most laptop batteries these days will give you between 3-6 hours of time before the power runs dry. The US AirForce Research Laboratory has been fooling around with betavoltaic power cells, which harness the power of nuclear decay to transmit power.
As radioactive material decays it lets off beta particles that can then be transformed into electric power. And it would produce enough energy to power a device for years, maybe even decades. — Andrew Dobrow