"In most energy-harvesting IoT devices, a supercapacitor will be augmented by a rechargeable battery for this reason. Often the battery will work by charging the supercapacitor at low power, then when power bursts are required, the supercapacitor can supply what’s needed. If the needed peak power exceeds the amount the battery can supply, then the battery can charge the supercapacitor at low power and the supercapacitor can deliver the high-power bursts. 

In this way, the benefits of rechargeable (i.e. Li-ion or Li-Po) batteries are combined with the benefits of supercapacitors in an IoT device. 

Xidas Claims the Best of Both Worlds 

Xidas, a company focused on IoT solutions, has pitched a novel design structure that could enhance the symbiotic benefits of rechargeable batteries and supercaps. Instead of separating a battery and a supercapacitor from one other, why not integrate both into one energy-storing device?" 

Xidas Creates New Battery Hybrid: Supercap and Rechargeable Lithium Battery - News (allaboutcircuits.com)