High-voltage CMOS (HV-CMOS) pixel technology is being considered for future Higgs factory experiments. The ATLASPix3.1 chip, with a pitch of 50 μm × 150 μm, fabricated using TSI 180 nm HV-CMOS technology, is a full reticle-size monolithic HV-CMOS sensor with shunt-low dropout (LDO) regulators that allow serial powering for multiple sensors. A beam test was conducted at DESY using 3–6 GeV electron beams, with chips operated in triggerless readout mode with zero suppression, demonstrating multi-chip capability. This was further evaluated with hadron beams, both with and without the built-in power regulators. This study presents the electrical characterisations of the shunt-LDO regulators for serial powering and test beam results of ATLASPix3.1 sensors.