Wearable devices continuously gain their popularity due to flexibility and opportunity to enable more applications and services, in particular, in healthcare industry. Guarantying long-term operation for these devices is among the key challenges at the design stage. In this work, we propose a multi-source energy harvesting system to address this problem. The proposed solution is based on two technologies namely an Enzymatic Biofuel Cell (BFC) and a low-temperature gradient Thermoelectric Generator (TEG) which are capable of generating power from human perspiration and heat, respectively. Upon designing BFC, we designed a functional circuit that combines it with the TEG. The resulting BFC has an output voltage of 200 mV and a power of about 7 nW. An array of BFCs is used as a source for initial push to start up the internal logical control circuit of the DC-DC controller. The low-temperature gradient TEG with an output voltage ranging from 40 mV to 70 mV and a constant measured output power of 160 uW is used together with the BFCs for energy harvesting upon the initial starting of the DC-DC controller.