Digital Voltage Meter for Milwaukee Battery Charger

I wanted to see what the voltage and current of my Milwaukee charger. The display toggles between the m12 side, m18 side and off by pushing the bottom upper right of the digital display. So far no current reading but the voltage is working well. I also made some tubes from a plastic pen body to concentrate the LED light upward instead of lighting up the entire inside. This is v1.0 and has room for improvement but thought I’d put it out there.

Supplies

Digital voltage display (lots of options here)
Razor blade
Wire strippers/crimpers
Red wire and ground wire
Wire connectors
Heat shrink
Rotary tool (careful not to slip)
Scissors
Button switch (I reused one from a Harbor Freight blue freebie flashlight)
T10 bit
Carbon fiber sticker (optional)
Old school standard plastic pen body
Foil tape
Hot glue gun (don’t judge me)
Solder and soldering iron (also no judging my soldering skills)

The Start

To make room for the digital display, cut off the the wording part of the label, I saved it and attached it to the side of the charger but had to use some spray adhesive to persuade it to stay in place. Then take the top half off and trim the corners down and pressing from the center out where the lower portion was. Next is disassemble, using the T10 bit, unscrew the four screws on the bottom of the charger and separate the two pieces. The m18 terminal will need to be wiggled out and the top half of the charger shell will be free.

LED Tubes

Measuring approximate height, cut the plastic pen body into two equal lengths that are short enough for the top shell to still fit without touching. Wrap the tube in foil tape and (remember no judging) hot glue them over each LED.

Cutting and Fitting

Measure on center of the top label area and using the rotary tool, cut an appropriate size hole to fit the meter. I also added a carbon fiber looking sticker for some extra jazz.

Selection Button

I used a push button I got from a Harbor Freight flashlight but there is a lot of options out there for switches and buttons. Also mounting location may vary depending on what you have. I cut out one vent slot and some of the body between the two docks with the rotary tool. Go slow here as to not slip. The bit I used had the tendency to grip causing more material that wanted to be cut. After some cleaning up and test fits. I used JB Weld to hold it in place.

Electrical

The charger board has two red output wires. I just removed some of the wire insulation and soldered a jumper wire on both. However it would be better to remove the wires from the board and splice in the wires, I plan on redoing this later. Measure the proper wire length to the voltage meter. Cut, strip, and crimp wire connectors. I soldered a ground jumper wire to the 12 v side. A shorter voltage meter would be nice, I had to bend the tabs to make the tight fit.

Finishing

After verifying all the connections, reassemble the charger and test it out. With the charger unplugged, the volt meter should read the the voltage of a battery when connected to the charger. If I was going to do this project again, I would have picked a different volt meter. Definitely something shorter, and probably one with a USB output due to the fact that the current is not reading.