Abstract: This invention provides a method and apparatus to prevent a battery or any one cell of a multi-celled battery from undergoing voltage reversals by disconnecting the battery from a load when the battery or one cell falls below predetermined reference potential levels. Means are provided for comparing the potential levels and disconnecting the load when the decreased potential levels are detected.

Abstract: A temperature sensitive liquid level controlling apparatus employs a pair of carbon resistors, each having a resistance which changes in response to immersion in a low temperature liquid, for determining upper and lower levels of the liquid in a container. The resistances of the resistors are compared with those of reference resistors to provide a signal for controlling a flow of the liquid into the container. A liquid cooling system incorporating this liquid level controlling apparatus displaces the liquid from a second container into the first-mentioned container by supplying a gaseous phase of the liquid into the second container, the signal being used to operate a two-way valve in the liquid passage for venting the second container through the liquid passage and for permitting the flow of the liquid from the second container through the liquid passage.