The Wouxun KG-UV6D is my choice of amateur radio hand held covering the 2m and 70cm amateur bands. The radio has worked beautifully for several years but lately it hasn't held a charge indicating the lithium iron battery needed replacing.
Looking on line for a battery I got side tracked and found adapters that clip in place of the battery that will convert the vehicle 12Volt down to the required 7.5Volt for the radio. This seemed a good idea for mobile use of the radio. These adapters are cheap but I thought I could make one, the main part I needed was the case to clip on the rear of the radio in place of the battery. If the battery could be removed from the case, then I would have the case I required.
Step 1: Opening the Battery.
The battery that clips on the rear of the radio was surprisingly easy to open. A sharp knife used carefully to score around the battery cover was all that was needed and the battery was accessible.
Using wire cutters, remove the battery.
Step 2: The Voltage Regulator.
Doing a search on ebay, (Adjustable Voltage Regulator Power Supply Module DC to DC 5V 12V 24V 3A) I found variable voltage regulators called Buck converters. Check out wikipedia Buck Converter for the technicalities on how they work but bottom line is they are 95% efficient so very little heat generated when dropping the voltage.
The one I purchased cost $8.00 AUD and fit the battery case perfectly.
Step 3: Fitting the Voltage Regulator.
Positioning the regulator in the case as shown meant the lid would fit if a hole was drilled for the voltage adjustment pot screw head to protrude. To find the position for the hole I took two photo's, one with the lid on and one off. In a photo editor like Gimp I could then super impose the lid photo over the case with no lid and drop the opacity of the lid photo, there by seeing the location of the potentiometer screw head. This idea sort of worked but as the two photo's were of differing sizes, I was out by 2mm. Done carefully it should work perfectly.
Next job was to wire the regulator to the 12V cigarette lighter plug and to the voltage contact pads on the old battery cover. I used a fused 12V cigarette lighter in case of a electrical short in the regulator or wiring and because that's what I had on hand.
I bolted the circuit board in but a glue gun would have worked just as well and easier too.
Step 4: Finishing the Job.
Wiring is straight forward. The board is marked with + connection for input and output. Once wired correctly, make sure + and - wiring is correct, plug into the cigarette lighter and using a volt meter, adjust the regulator potentiometer until an output voltage of 7.5Volts is measured at the gold contact pads on the battery case lid. I used a piece of electrical tape on one of the metal capacitors as there was a risk it may touch the contact pad if the regulator moved. Glue the battery cover in place although once the battery case is clipped on the radio it should stay put but glue to be sure.
Testing the radio on receive and transmit and all seems to work beautifully. There seems to be a slight voltage lag when the radio is first turned on that shows on the radio's screen like a low battery. I think the regulator is slow to respond to the sudden current requirement. I will try a 25uf capacitor across the output of the regulator next time I open the battery case containing the regulator. It works ok as is, but I think this fix maybe worth doing.