Baofeng UV-82 direct charging ( without cradle)

I have a couple of UV-82 radios with the thicker batteries with the direct charging port on the battery. Don’t have the USB direct charging cable. I’d like to make something a bit more robust than the available usb charge cables. I’m figuring the charge cable just supplies a certain voltage and the battery has the charging circuit in it to manage the charging of battery. Can anyone tell me what voltage I need to supply here? Assuming my assumption about just needing to supply correct voltage is correct.