Membraneless microfluidic fuel cells (M²FCs) are promising portable power sources, but they suffer from limited scalability. This paper presents a scaling-out strategy for general M²FC applications with their characteristics studied by both experiments and mathematical modeling. The present strategy addresses the issues of flow distribution non-uniformity and shunt current losses by integrating a well-designed fluid circuit. With the present strategy, parallel and series connections of four cells in an array results in a scaling-out efficiency of 93% and 82%, respectively. The effects of different parameters on the array performance as well as further device scalability are also investigated in this paper. Preferable conditions for the array operation include a high branch ionic resistance, small unit cell difference and high unit-cell performance, which can be achieved by appropriately designing the branch geometry, employing high-precision fabrication/assembly techniques and improving the single-cell materials/chemistries. It is expected that the present array can be incremented to 50 cells or above in series with over 75% efficiency as long as there is sufficiently high branch resistance or cell performance.