The standard charger accompanying a Baofeng UV-5R or DM-5R comes with a 10V wall adapter. While it is lightweight it is yet another item to bring along with the radio.
I decided to modify the charger cradle to support USB input instead. I drilled a hole to mount a spare USB cable I had around and and fixed it with some hot glue. To safeguard the USB port I installed a 1A fuse in series with the 5V (red) wire of the USB cable.
I then installed a small $1 DC converter from ebay sold under the name
DC Boost Step Up Regulator Power Module Micro USB 2~24V to 5~28V 2A Adjustable. I adjusted this to 10V before soldering the
OUT leads to the charging circuit. It may need a small readjustment after this.
I decided that I will not use the original wall adapter in the future, so I just filled the charger cradle DC input connector with hot glue as well. If you wish to be able to use both the adapter and USB for charging, I recommend that you add a small diode such as 1N4007 in series with the red
OUT' wire to ensure that you do not fry the DC converter circuit when connecting the wall adapter. Adding the diode results in a voltage drop of about 0.7V, so you will need to adjust the DC converter
OUT voltage to 10.7V to get 10.0V at the charging circuit input.
You can see the result above. Using a USB meter (uncalibrated) I charged a new original Baofeng BL-5 battery with 7.4V 2000mAh/14.8Wh printed on the back. The DC converter
OUT provided roughly the same voltage and current as the wall adapter, and the charging time was therefore the same as when using the wall adapter. The USB current was about 0.95A most of the time.
When finished the charger had consumed about 4000 mAh, so you will need a USB battery pack of this capacity to get a full recharge of your Baofeng radio. If you have added the diode to enable using the wall charger as well, you can expect that a full charge consumes about 280 mAh (7%) more on a full recharge.