Maximum efficiency at low input voltages and currents is key in energy harvesting operations. This efficiency chart shows the bq25504 efficiency over a range of energy source input voltages using an actual bq25504 device and evaluation board in TI’s engineering lab. The 3 circled areas indicate efficiencies for various energy source elements such as a TEG, which typically has very low input voltages; single cell solar panels, typically having output voltages up to 0.5 V; and multiple cell solar panels with output voltages in multiples of the single cell solar panel. The 3 colored graph lines indicate various energy storage voltages and illustrate similar efficiency expectations.