Voltmeter housing
thingiverse
I've got a bunch of these lying around, made with various connectors to match whatever battery I'm measuring. Each one gets its own designated spot - there's one in my FPV-drone box, another in the RC cars' storage container, and even one right next to the battery charger. It was specifically designed for this digital voltmeter: http://www.banggood.com/0_28-Inch-2_5V-30V-Mini-Digital-Voltmeter-p-974258.html. Before sealing each unit, I add a dash of UHU patafix glue pads to ensure it stays secure but remains easy to open up and adjust the voltage level as needed.
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