The Boafeng UV3R dual band ham radio uses a small 3.7v lithum battery. The radio comes battery charger and a wall 110v to 5vdc wall wart/Dongle. When I opened up the charger there was no active devices, Just the 5v from the wall wart directly into the battery. I wanted to convert charger to USB and add some smart charging to the device.
While this project was written for a Baofeng UV3R ham radio the functional changes could be applied to other radio's and devices that use a single lithum battery.
Stock UV3R charger base.
Mini USB 5V 1A Lithium Battery Charging Board
The can be found on ebay. Search for "USB Lithium Battery Charging Board" will return a number of board options. Note some come with mini USB and some come with micro USB connections. get the one that suits your needs.
Red and black wire makes it easy to identify the polarity, but any wire will work.
I have been charging my uv3 via USB for a couple of months now and its working great. The additon of the hole to see the charger state really helped to know if it was charaged. Overall its worked out as a nice mod to the radio.
The project didnt take more than 30 minutes of time once I had the charger board. there is a lot of room in the charger case so no critical tolerances to worry about. Only a few connections to solder so this should be an easy project for even those inexperienced in soldering.
Remove the 3 screws from the bottom of the charger base. They might be covered with stickers or rubber feet.
Open up case carfully as the wires inside are short. Your going to remove them but you need to know where they go to. Mark the positive and negative terminal. NOTE: The AC power connection uses center ground and shield positive.
Determine where your charger board will fit. Make sure there is room for the connection when closed. For most boards you should be able to place it under the radio cup.