I would like to first apologies in advance if my instructions are not clear, as this is my first time posting an Intractable. After seeing a similar gadget that looked alike it required a lot more work without the added feature of having a battery indicator built in I decided to post mine. Please feel free to ask any questions especially if you have a hard time understanding my instructions.
Step 1: What You Will Need
Ryobi Model # P150 18-Volt One Plus Battery Fuel Gauge
GTMax Mini USB Car Charger Vehicle Power Adapter - Black for Apple iPhone 4 4G 16GB / 32GB 4th Generation
Soldiering supplies, A short peace of small wiring I used 20 gage wire.
Optional Supplies, Wire stripers, a wood burning kit with exactor blade tip for cutting the plastic case.
Step 2: Prepping the Battery Gage
(1.) Carefully remove the sticker so that you can reapply it at the end.
(2) Remove the 4 screws holding the unit together I used a 3.5 mm philips head screwdriver.
(3) After taking out the 4 screws the unit should come apart easily.
(4) You then can remove the circuit board and components buy lifting it straight out.
Step 3: Prepping the USB Charger
(1) Unscrew the 2 Philips screws on face of the unit one will be under the label.
(2) Remove the metal faceplate
(3) unscrew the end of the charger and remove the fuse and spring
(4) The circuit board should lift right out.
Step 4: Prepping the USB Charger Continued
(5) You should be able to lift the Metal flares on the Negative side right off.
(Optional) I removed the LED since I did not see a need to have it and I didn't want to have to redirect it or cut a small hole for it.
Step 5: Soldiering
Refer to Picture Notes
Step 6: Soldier the Power Leads
Above each post there are three points of contact with the circuit board that create a triangle it doesn't matter which of the three points you soldier your connection to so witch ever one looks easiest.
If you are looking at it with the center post closest to you then the left post is negative and right post is positive.
After making the connection I feed the wire down the already existing holes with the negative throw the top hole and the positive throw the bottom hole
Step 7: Marking Where to Cut
You won't to be as snug as possible without smashing the USB connection so that it will stay in place. I found that by plugging a USB cable into the plug you can prevent it from getting warped or bent since they tend to be fairly fragile.
You can always cut more away it's a little trickier to add it back
Step 8: Cutting the Case
I used a woodburning tool with an X-Acto blade to cut the plastic easily.
Depending on your usb car charger that you use you may need to cut the opening at an angle to accommodate for the short standoff distance from the circuit board to the lip of the USB plug I found that the plastic was thicker than the distance I had so I had to cut it at an angle to allow room for the circuit board to come closer to the opening allowing the USB metal flare to catch the plastic.
Step 9: Putting It All Together
It works grate and the battery gage works flawlessly!
It can be a little tricky to get the hole to tightly line up while not warping the plug I strongly suggest plugging a cable into it to ensure that nothing gets warped. It also gives you more control when positioning the plug since you having something to hold onto.
I am sorry I didn't take more pictures of me putting it together I got carried away with finishing and forgot I guess it's something you have to get use to when making instructions. If if will help anyone I can open if back up and take some pictures of it inside the case with one side off to give a better idea of how it fits in there