This compact and robust device optionally displays the two voltages of the on-board battery and the starter battery. It clearly displays the most interesting range of battery voltage from deep discharge to maximum charging voltage. The illuminated dot display provides a very accurate indication of the battery voltages, as intermediate values are also easy to read due to neighbouring illuminated dots of different brightness. The on-board or starter battery voltage can be selected or the display switched off at the touch of a button. When the battery voltage is low, red indicators indicate that the battery needs to be recharged. The connection is made via screw terminals on the back of the device. The Duo Battery Tester S is designed as a panel version to match the VOTRONIC module system and fits in perfectly with other VOTRONIC display panels (standardised height 85 mm). Of course, it is also possible to retrofit a single display in the vehicle. Small front panel dimensions and the particularly low installation depth of just 15 mm allow installation in almost any position, and the storage space behind the panel can still be used.