This was a quickie project for checking LIPO voltages before parallel charging and can also check individual cell voltages of multi-cell batteries or anything using a 0.1" pitch connector. I already had one of the cheapie chinese LED voltmeters and just designed the 3D printed housing and added the test prongs.
I’m not going into too much constructional detail as it’s all fairly obvious. It uses two pins of a header strip for the prongs, and the red and yellow wires are connected together so the battery under test is also supplying the DVM supply voltage. The red and black markings are small pieces of 1.75mm filament pressed into the slots. The LED display is 22.5mm x 10mm…
The voltmeter is reverse polarity protected, so no need for extra circuitry. Chop the mounting ‘ears’ off as they’re not needed.
Before inserting the display in the case, decide which hand you’re going to hold the meter in and orient it accordingly.
Two pins of a 0.1" pitch header. Trim the plastic off the sides.
Header should be a tight fit, pressed into the case. Red wire goes to the +V and the measurement pin.
All sealed up with hot glue. I tested this first to see if hot glue melted the PLA, but it was fine.
The finished tester.
Use the JST connector to check the overall battery voltage.
Poke the prongs into any adjacent pins of the balance plug to check individual cell voltages.