One or more switches 208 and 209 can each include a plurality of individually controllable switches that alternate connection between the second and third battery for charging and/or discharging the second and third battery. For example, when the second battery reaches a threshold charge (e.g., becomes ‘full’), the charge circuit to the second battery can be opened and a charge circuit to the third battery can be closed. As such, thermal energy can continue to be harvested by the third battery when the second battery becomes full.

Similarly, the second battery can be connected to power the IT equipment. When the second battery discharges to a certain threshold (e.g., 10% remaining capacity or less), the third battery can be connected to the IT equipment to take the second battery's place. The controller can measure capacity based on open voltage readings of batteries and/or current monitoring.

It should be noted that, in FIG. 2, some power electronic circuits such as converters that convert AC/DC from the power source 230 to the batteries are not shown. Similarly, inverters that convert DC voltage from the batteries to AC voltage to power the IT equipment are not shown. Such converters can comprise power switching devices (e.g., mosfets, transistors, IGBTs, and/or other semi-conductor devices), diodes, capacitors, resistors, inductors, and other passive or active electronic components that are arranged in a converter circuit to actively rectify an AC voltage source to DC voltage, or convert a DC voltage to another DC voltage (e.g., a boost converter). An inverter can also include such electronic components arranged in an inverter circuit to convert DC voltage to AC voltage.