This instrument is designed to be suitable for use by electrical installation contractors and as such is a robust meter having a stabilized power supply, thus requiring no zero adjustment, etc. after initial calibration by the Manufacturer. However, it is inevitable that normal wear and tear will eventually cause the performance of the instrument to deteriorate. BM7 Battery MEGGER testers use an electronically generated test voltage, which is energised only while TEST button is pressed. One hand operation. Automatic discharge of circuit capacitance. On-load battery check. Taut-band, moving coil movement.