This paper reports an easy-to-fabricate micro battery that can be directly printed on a bio-sensing device such as an immunoreaction-based disposable complementary metal oxide semiconductor bio-sensing chip. The printed Mg and AgCl films were used as both cathode and anode materials, while the inspection solution for the bio-sensing was utilized as an electrolyte, which simplified the structure of the battery. A micro battery fabricated on the printed circuit board, in which each electrode size was 3 x 3 mm(2), could generate an open circuit voltage as high as 1.58 V, a maximum power as high as 1.4 mW and a total stored energy as high as 400 mJ. Wireless sensor test platforms self-powered by the developed on-chip battery successfully worked in a 0.14 M NaCl solution, and digital data could be successfully transferred using both optical and capacitive coupling methods. (c) 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.