Battery management systems and methods

A battery management system includes thermal batteries, sensors, a clock, a processor, and memory storing a data structure, and is configured to receive energy parameters and time data, calculate a rate of energy usage of the thermal batteries based on the received data, and execute battery commands to activate or disable selected thermal batteries. Energy usage data can be stored as individual data points over time, and battery commands can be received from an external computer. The system determines when to activate a second battery based on a predetermined threshold of estimated electrical energy of a first thermal battery. A battery management method includes receiving signals for voltage, current, temperature, and time duration, estimating electrical energy based on these parameters, and activating a second battery when the estimated energy falls below a predetermined threshold.