VISO oscilloscope uses an internal Li-Ion 3.7 volts battery. You do not need to connect it to 24 volts. You have to use DC 5V power charger to charge the battery.
CarScope Viso offers two methods for relative compression test: DC current and AC voltage. More you may read here: autoditex.com/page/relative-compression-test-67-1.html
@Elmer Simon Thank you for your interest in our products! This is the page with our distributors: autoditex.com/page/contact-us-5-3.html This is CarScope Viso eBay page : www.ebay.com/itm/CarScope-Viso-automotive-oscilloscope-Automotive-Diagnostic-Oscilloscope/253884497448?hash=item3b1cb1fe28:g:8RgAAOSwi0RX0YSg:rk:2:pf:0