Source efficiency in planar betavoltaic batteries is drastically reduced by self-absorption and directional loss. In this paper, we present a technique of improving source efficiency by the use of beta particles reflectors based on metals. A metallic layer with a high atomic number is an effective electron reflector, capable of reflecting up to 50% of the escaping energy from the backside of a source and they are more efficient for thinner radioactive layers. The obtained results show that the design of separate planar one-sided sources with electron reflectors could be optimized to reach high efficiency before assembly with semiconductor converters. Using Pb reflector for a 200 nm thick Ni-63 source 38.5% of directional lost energy could be recovered. They can lead to a cost-effective technology compared to sandwiched, porous, or three-dimension microstructure designs.